I am not a pro, just a newbie. I just wrote some code doing what you want to do. This may not be the best way to go, but it's very easy. All you have to do is to check if a file/folder exist in a directory that you know it should when the software is installed
If System.IO.File.Exists("C:\Program Files\Microsoft Visual Studio 10.0\Common7\IDE\vsdiag_regwcf.exe") = True then
P.S. Win7 install path is not the same as WinXP. So you can test both.