I was trying to run "aspnet_regiis -ga domain\user" from the command prompt today, but it wouldn't work! I was trying to add calsvdafran03\VSeWSS local user to IIS 7.0 on Windows 2008 Server so that I could take advantage of Visual Studio 2008 extensions for Windows SharePoint Services 3.0, v1.3. The 64 bit version that is. Anyway, I ran into difficulties running it and then discovered that I had to navigate to the C:\Windows\Microsoft.NET\Framework64\v2.0.50727 directory in order to successfully execute the command.