Hi
I too do a fair amount of video work. You need to make sure your hard drive is up to the task - check your event logs and see if there is an event that tells you what has caused the problem.
Also, even if your hard drive specs are sufficient, I would still make sure that the drive itself is healthy. I was using a new 120GB SATA drive for converting multi-gigabyte AVI's into WMV's, but the drive was bad and the PC kept hanging. Replacing the drive has solved my problem.
Also, as above, I normally allow the program to run on its own - there is no point in trying to do anything else.
If you want to multi-task you will need a very powerful PC - several processors, heaps of superfast RAM, SCSI drives etc etc
One other thing - are you using a separate drive for this, or are you using the system drive? If the latter, I really recommend that you purchase a separate drive otherwise you risk breaking your PC.
Good luck