Hey Jared,
About the whole windows xp/windows 7 upgrade creating a lag. I have the same issue..
Used to work on a 32-bit vista system with cs4. Always converted to cineform and thge files edited fine, no lag at all.
I then upgraded to windows 7 32-bit, which created an alltogether better system performance, except in cs4.. playback of the same files creates a lag..