If the OP can't afford an upgrade then examination of the HD would be in order. And, if the OP doesn't have a spare drive bay then bigger issues are at hand when doing a drive replacement. 20 gb of free space should be more than enough, depending on the length of a video production. It could take 1 gb for every five minutes of video.
Bruce,
I would love to have dual 320's on my laptop but I didn't want to spend the extra $300.
I agree on getting rid of the junk on a hard drive, but it is highly unlikely that the OP will get rid of enough junk to do more than one production.
320 GB hard drives are around $65 right now. I remember paying $350 for a 300 MB hard drive about 14 years ago, and at that price, it was a steal.

And, as far as 20 GB being enough space, it would be for the temp files when encoding.
Thank You all for the prompt replies. I only have 500MB, yes megabytes of Hard Drive space left. I'll move some files to a back up hard drive. However, I do not have this "temporary files" problem anymore. I have a new problem which I posted on a new problem. Cheers!
You are doomed for any video work then. I would bet that you can't even defrag that hard drive, because there isn't enough space to do it.
Once your hard drive gets down to between 10% and 15% space left, if you do get it to defrag, it will take a long time to do it.