Agreed. Use another hard drive preferrebly on the 2nd ide channel (you might have to swap CD drives or something).
I'm editing video with one hard drive but my problem is RAM. I have 512mb and when playing with a long video, it quickly tops out and uses the swap file. And THAT can be a problem as well. Go cntrl-alt-delete and look at your task mgr. If you're going over your physical limit, you're bogging down the PC. I suggest at least a gig of ram for video editing. Also, get good ram like Mushkin HP, Kingston HyperX or Corsair XMS.