I encountered this problem last week, wherein the LINQ project templates were missing in the "New Project" dialog of VS2005 Team System even after doing "everything" (machine reboot, "install IDE support", etc.). By searching the web (through the help of our trusty buddy, "google"), i was able to determine that the LINQ project templates files were:
[C#]
Console.zip
Library.zip
LINQWebSite.zip
WinForms.zip
WinFX.zip
DLinqObjects_CS (item template)
[VB]
LINQ Console Application.zip
LINQ Class Library.zip
LINQ Web Application.zip
LINQ Windows Applicztion.zip
DLinqObjects_VB.zip (item template)
After obtaining the information, all I had to do now was to determine where to place the said files. After some searching within "Program Files\Microsoft Visual Studio 8" I eventually found the place:
<drive>:\Program Files\Microsoft Visual Studio 8\Common7\IDE\Project Templates
There's a folder for each language, just place the appropriate files in the appropriate language folder. If you want the templates in their own "category display" within the "New Project" dialog of Visual Studio, just create a subfolder in the language folder. In my case, I created a "LINQ Preview" subfolder under "CSharp" and placed the files there.
I did the same thing for the DLinqObjects_CS.zip file, but i placed it in the appropriate subfolder under "Item Templates" instead of "Project Templates".
As a side note, I'd like to mention that I never encountered this problem when I was still using Visual C# 2005 Express Edition. Weird.
I hope somebody finds this helpful/useful.