There are one or two other threads right now that cover it in more detail. The easy way is to capture a bit of the noise with some noise reduction filter. SoFo has a good one (but expensive) others out there as well. They all work on the sample principle.

1. identify the 'noise'
2. capute a noise print
3. modify the filter, apply.

I wrote a tutorial some time back. Not an example of my best work, had a bad cold at the time, but you can get an idea of what's involved.

http://www.vegasusers.com/vidshare/?s=d&t=150

Near the bottom of above page.

I actually didn't follow my own advice that well. If you listen to the finished portion you can hear artifacts, sounds tinny and some haromincs in there. These crept in because I applied the filter TOO STRONGLY, (I guess my ears were stuffed up too, didn't sound as bad to me as it does now) and I didn't set the attack and decay right either. Oh well, gives a good example of over doing it. Got to do a better tutorial one of these days.