there are some lengthy discussions on how to best import files from endnote,
http://forums.zotero.org/discussion/70/importing-endnote-files-into-zotero
but the bottom line of all of them is that you can't import .enl (endnotes library format) styles. You will, unfortunately, have to find a way to get your EN library in RIS format.
Maybe ask a friend? A local University Library/librarian? Maybe even a mailing list?

This also came as error with the RIS export attempt:

"[JavaScript Error: "undefined entity" {file: "http://news.nationalgeographic.com/index.rss" line: 39 column: 571 source: " <description><table cellspacing="0" cellpadding="1"> <tr> <td valign="top"> <a href="http://news.nationalgeographic.com/news/2009/03/090316-st-patricks-day-facts.html?source=rss">; <img src="http://news.nationalgeographic.com/news/images/thumbs/090316-st-patricks-day-facts_60x40.jpg"; height="40" width="60" alt="image" /> </a> </td> <td valign="top"> <p>Few celebrating St. Patrick's Day—Tuesday, March 17—know much about the man and the myth behind the holiday that turns rivers green and makes Guinness flow.</p> </td> </tr></table></description>"}]

[JavaScript Error: "not well-formed" {file: "http://www.anthrosource.net/404.aspx?404;http://www.anthrosource.net:80/action/showFeed?ai=rs&jc=aa&type=etoc&feed=rss" line: 105 column: 108 source: " <li><a href="http://www.blackwellpublishing.com/librarians/librecfm.asp?ref=ANTH-SOUR&title=AnthroSource">Recommend to a Librarian</a></li>"}]

[JavaScript Error: "mismatched tag. Expected: </img>." {file: "http://english.aljazeera.net/" line: 22 column: 103 source: " <img border="0" src="/Media/Images/AJILogo.jpg" width="94" height="100"></a>"}]

[JavaScript Error: "this._processor is null" {file: "file:///C:/Program%20Files/Mozilla%20Firefox/components/nsLivemarkService.js" line: 934}]

[JavaScript Error: "this._processor is null" {file: "file:///C:/Program%20Files/Mozilla%20Firefox/components/nsLivemarkService.js" line: 934}]

[JavaScript Error: "out of memory" {file: "chrome://zotero/content/xpcom/notifier.js" line: 136}]

[JavaScript Error: "syntax error" {file: "http://forums.zotero.org/extensions/PreviewPost/ajax.php" line: 1 column: 1 source: "Hello Adam. I;ve tried importing a 3400 reference list from Endnote using the RIS and the BibTex export formats. In both cases it doesnt work - in the former case firefox gave an error:"Add-ons: {d10d0bf8-f5b5-c8b4-a8b2-2b9879e08c5d}:1.0.1,{ca0849e8-2c76-42ae-9abe-34e14d337acf}:1.77,ctrl-tab@design-noir.de:0.19.3,{d37dc5d0-431d-44e5-8c91-49419370caa1}:2.5.11,foxmarks@kei.com:2.7.2,{BCC877E7-7F3F-4632-8338-DAEE4475DE35}:0.16,{77b819fa-95ad-4f2c-ac7c-486b356188a9}:1.5.20090207,{1A2D0EC4-75F5-4c91-89C4-3656F6E44B68}:0.3.1,{CAFEEFAC-0016-0000-0012-ABCDEFFEDCBA}:6.0.12,jqs@sun.com:1.0,{06997db0-c027-4d5f-bd37-b0d9230226ea}:0.52,translator@dontfollowme.net:1.0.4.4,zotero@chnm.gmu.edu:1.0.9,{972ce4c6-7e08-4474-a285-3208198ce6fd}:3.0.7<br />BuildID: 2009021910<br />Comments: this happende through iimporting a 3000+ reference list in RIS format to the Zotero add on<br />CrashTime: 1237285820<br />Email: maa27@cam.ac.uk<br />InstallTime: 1236335804<br />ProductName: Firefox<br />SecondsSinceLastCrash: 1110700<br />StartupTime: 1237284031<br />Theme: classic/1.0<br />URL: <a href="http://forums.zotero.org/discussion/70/importing-endnote-files-into-zotero" rel="nofollow">http://forums.zotero.org/discussion/70/importing-endnote-files-into-zotero</a><br />Vendor: Mozilla<br />Version: 3.0.7<br /><br />This report also contains technical information about the state of the application when it crashed."<br /><br />in the latter firefox crashed"}]

[JavaScript Error: "not well-formed" {file: "http://www.anthrosource.net/action/showFeed?ai=rs&jc=aa&type=etoc&feed=rss" line: 105 column: 108 source: " <li><a href="http://www.blackwellpublishing.com/librarians/librecfm.asp?ref=ANTH-SOUR&title=AnthroSource">Recommend to a Librarian</a></li>"}]

[JavaScript Error: "mismatched tag. Expected: </img>." {file: "http://english.aljazeera.net/" line: 22 column: 103 source: " <img border="0" src="/Media/Images/AJILogo.jpg" width="94" height="100"></a>"}]

[JavaScript Error: "this._processor is null" {file: "file:///C:/Program%20Files/Mozilla%20Firefox/components/nsLivemarkService.js" line: 934}]

[JavaScript Error: "syntax error" {file: "http://forums.zotero.org/extensions/PreviewPost/ajax.php" line: 1 column: 1 source: "Hello <br /><br />I;ve tried importing a 3900 reference list from Endnote using the RIS and the BibTex export formats. In both cases it doesnt work - in the former case firefox gave an error:<br /><br />"Add-ons: {d10d0bf8-f5b5-c8b4-a8b2-2b9879e08c5d}:1.0.1,{ca0849e8-2c76-42ae-9abe-34e14d337acf}:1.77,ctrl-tab@design-noir.de:0.19.3,{d37dc5d0-431d-44e5-8c91-49419370caa1}:2.5.11,foxmarks@kei.com:2.7.2,{BCC877E7-7F3F-4632-8338-DAEE4475DE35}:0.16,{77b819fa-95ad-4f2c-ac7c-486b356188a9}:1.5.20090207,{1A2D0EC4-75F5-4c91-89C4-3656F6E44B68}:0.3.1,{CAFEEFAC-0016-0000-0012-ABCDEFFEDCBA}:6.0.12,jqs@sun.com:1.0,{06997db0-c027-4d5f-bd37-b0d9230226ea}:0.52,translator@dontfollowme.net:1.0.4.4,zotero@chnm.gmu.edu:1.0.9,{972ce4c6-7e08-4474-a285-3208198ce6fd}:3.0.7<br />BuildID: 2009021910<br />Comments: this happende through iimporting a 3000+ reference list in RIS format to the Zotero add on<br />CrashTime: 1237285820<br />Email: <br />InstallTime: 1236335804<br />ProductName: Firefox<br />SecondsSinceLastCrash: 1110700<br />StartupTime: 1237284031<br />Theme: classic/1.0<br />URL: <a href="http://forums.zotero.org/discussion/70/importing-endnote-files-into-zotero" rel="nofollow">http://forums.zotero.org/discussion/70/importing-endnote-files-into-zotero</a><br />Vendor: Mozilla<br />Version: 3.0.7<br /><br />This report also contains technical information about the state of the application when it crashed."<br /><br />in the latter firefox stalls for a very long time (Im talking 20 minutes or so), with a progress bar still going (BTW what's the point of a progress bar if it doesn't show an accurate representation of the volume of work to do) and then reports that it was not possible to import.<br /><br />Total length of these tests: 40 minutes. <br /><br />I love the idea of moving to zotero and getting rid of word and use open office - however, I cannot seem to make it all work for me.... Any help will be appreciated. Feel free to ask for a copy of the Endnote file.<br /><br />best<br /><br />m."}]

[JavaScript Error: "mismatched tag. Expected: </img>." {file: "http://english.aljazeera.net/" line: 22 column: 103 source: " <img border="0" src="/Media/Images/AJILogo.jpg" width="94" height="100"></a>"}]

[JavaScript Error: "this._processor is null" {file: "file:///C:/Program%20Files/Mozilla%20Firefox/components/nsLivemarkService.js" line: 934}]"

more than annoying it isa pity - I have been waiting for a stable version to try this on since I first heard about Z in 2007 - I still cant get it to work for me