Claude,

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework\policy\v1.0

If REG_SZ value 3705 exists, then dotnet 1.0 is installed.

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework\policy\v1.1

If REG_SZ value 4322 then dotnet 1.1 is installed. The official MS Redistributing the .NET Framework 1.1 documentation suggests you look at the following registry entry for a (DWORD) Install entry value of 1.

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\NET Framework Setup\NDP\v1.1.4322

I guess the same is true if you look a the following for dotnet 1.0.

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\NET Framework Setup\NDP\v1.1.3705

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnnetdep/html/redistdeploy1_1.asp

Regards
Neil