GTP4 can open .cwp files from older projects. The .cwp files only include project information, and pointers to your audio files, but not the actual audio files. Be sure to move those forward to the new machine.
If you still have the old PC, you might want to save your projects as .cwb (bundle files). These do include the audio.
You may still have to do some fiddling, but for the most part, you should be ok.
Be sure to update the Omega drivers for W7.