Random stalling or freezing on OS9.1

[eyedesign]

I hope some one can help. My system randomly stalls or freezes for a few to 20 seconds (never the same time laps) then frees up or at times will freeze all together and I have to restart. The freezes are random. I have had this problem with another system and I did a reinstall but it did not fix the problem. I believe it was caused by a file that was given to me on disc from a job I was doing work for but I can't be sure. Is there any way I could find out? The virus scan did not pick it up. It is very annoying. I also noticed a similar thing on a G5 that I believe the problem came from. The cursor jumps on the G5. Any one come across anything like this?