Most programs will by default install to the C drive. The best thing to do is to use custom install and select the other drive for each program that you want to install.
Windows 7 is a bit more complex and MS does not recommend using registry changes to change default program install location:
http://support.microsoft.com/kb/933700
With older OSs you could just alter the programfilesdir, but AFAIK that doesn't work as there are other keys for the x86 programs, and also other keys affected in the registry values: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion, like CommonFilesDir keys among others. If you go that way, be absolutely sure to back up all your important data and starting registry.
Reinstall a program to the path you want after you delete the version on C, but don't try to just move them and change registry path keys.