(Copy of my reply from the other post):
It could be because PSP can't access enough RAM to run smoothly because it's a 32 bit program trying to run video files that are best suited for a 64 bit environment.
If you have a 64 bit OS and have more than 4GB of RAM on your system you can try the utility on the page linked below. It might help with your problem. If you are unsure about running the utility, make a copy of the exe file onto a thumb drive before running it. That way you can delete the patched exe file and put back the original, no harm done.
http://www.ntcore.com/4gb_patch.phpJoe