Ok, so if I understand you correctly, you are saying that though you are able to use the 3.5 framework version of ajaxtoolkit, it doesn't work with ExtJs tabs (the content is hidden if ExtJs tabs are enabled). This is really the main thing I was wanting to find out. More and more I've been having various problems with ExtJs tabs, problems with display in Firefox 3, problems when using an FCKeditor in more than 1 tab. Since the new version of ExtJs has changed the license to GPL, I can no longer upgrade to new versions of ExtJs.
So I'm thinking of switching to YUI tabs everywhere that we are currently using ExtJs tabs. YUI tabs has worked for me in a few places where I've tried it where ExtJs didn't work well. Once I have switched it, you can tell me if it works with the .NET 3.5 version of ajaxtoolkit.
I have added a folder under _libs with the 3.5 versions of ajaxtoolkit and enterprise blocks 4.0. We have not been able to use enterprise block historically due to the license but in the 4.0 release they changed to MsPl license which is compatible. I still can't use it in the core of mojoportal until we change the target runtime to 3.5. Not sure yet when we will do that but it is only a matter of time.
Best,
Joe