Right click on the toolbox and go to "Show All" to make sure they are indeed in the toolbox.  If they are not there add them by creating a toolbox tab and going to "Choose Items...".  If they are there, is this only happening for Windows Forms or ASP.NET?  If its just ASP.NET, then make sure that the website you created is using the appropriate CLR for the NetAdvantage you installed.  So if you created a CLR 3.5 website, make sure you installed NetAdvantage 2008 Volume 2 for CLR3.x and vice versa for CLR2.0.  There is also another cause for the just the ASP.NET controls not appearing and it relates to your mouse.  You can find more information here:

http://www.west-wind.net/WebLog/posts/279041.aspx

If none of that helps, try creating a new website and just let it sit there and let visual studio figure out that there are applicable controls in the toolbox.  I was running into the same issue on this machine earlier today, and when i check visual studio 5 to 10 mins later while I was off doing something, the controls were no longer grayed out.