Protools running laggy after format

[Chombo]

OK, so i found the standard vga driver and installed it, it didnt change anything, however from doing some experiments and searching forums i have come up with some more hopefully useful info.

i found out that quicktime codecs could affect choppyness of protools, so i exported the video file as a motion JPEG A file and reimported it. nothing happened, it was just as slow and choppy.

However,

i have started a new session with a new project on a different short film and i have different symptoms. I started the session by importing an OMF into Protools LE 8.0 on my MACBOOK with am MBOX Micro, did some minor edits, everything was extremely smooth and perfect.

then i decided to see how it runs on my PC with XP, on Mpowered 7.4. it was extremely choppy again, but, the movie was using the codec "H.264, ACC, Timecode". i checked the System Usage and it was VERY SMALL, the meter was only a few millimeters. There was also a constant crackling and popping through out playback.

I then exported the video file using the Motion JPEG A Codec and reimported it to the session. it completely fixed the copppyness and it was smooth to work in, BUT, there was still the constant underlying crackling and popping through out the entire session during playback.

also the difference between my original project from the first post and my new project is the first one was 45 minutes long, my second project was only 5 minutes long.

Differences:
Project A (original post) wavefiles were imported into PC, using XP into M-powered 7.4. video file is 45 minutes long and using codec Motion Jpeg A. its extremely slow and choppy and CPU usage is about 70%.

Project B. imported OMF into PT LE 8.0 on MACBOOK, Was extremely smooth. Converted video file from H.264 to Motion JPEG A, and opened it up into PC, using XP into M-powered 7.4. Now it runs smooth, NOT choppy, BUT there is a constant crackling and popping throughout the playback and CPU Usage is at about 2%.

using this info is there anything anyone can determine? did converting the Project B session cause the crackling?