How to find the Service Pack of .NET Framework installed:
Klaus Bjørn Jensen 17-07-2008
Check the version of mscorwks.dll.Not every file in the framework/runtime gets patched in a service pack or hotfix, but mscorwks.dll is the core DLL of the CLR/runtime so that gets patched in any CLR hotfix.
Go to C:\WINNT\Microsoft.NET\Framework\Select the corresponding Version (1.0 or 1.1 or 2.0 ...) then find a file with the Name "mscorwks.dll" right click & go for Properties & Version
This is a list the key build numbers for the CLR:
1.0.3705.0 1.0 RTM
1.0.3705.209 1.0 SP1
1.0.3705.288 1.0 SP2
1.0.3705.6018 1.0 SP3
1.0.3705.6060 1.0 + MS07-040
1.1.4322.573 1.1 RTM
1.1.4322.2032 1.1 SP1
1.1.4322.2407 1.1 + MS07-040
1.1.4322.2300 1.1 with Windows Server 2003 SP1
2.0.50727.42 2.0 RTM
2.0.50727.312 2.0 Included with Vista
2.0.50727.832 MS07-040
2.0.50727.1433 2.0 SP1
See also: http://blogs.msdn.com/dougste/archive/2007/09/06/version-history-of-the-clr-2-0.aspx