I just added a friend of mine's 2.4 celeron (I OC'd it to 2.65GhzMyth: WIll it cost me a lot money in power:
Truth: At most a folding boxen will take around $5/month to run, but most people already run their PCs 24/7 so at most it will cost an extra $1/month. $1 is not much for all the great scientific research you computer is doing.
Myth: Folding could install spyware on my machine
Truth: After the initial client is installed, all Stanford will send you is a work unit that is only a few kilobytes in size, everything is encrypted and checked to be sure the content is from Stanford.
Myth: Folding will take up all my resources and it'll slow down my PC
Truth: Folding only uses spare cycles that you aren't using. It's CPU priority is usually idle (unless you set it otherwise). Your mouse and keyboard have more priority over your CPU than folding@home does. As for RAM, as long as you aren't running QMD's and other large memory hogg WUs, F@H is very easy on system memory, my machine I surf on only has 384mb and still crunches big WUs and I see no issues on it at all.
QMDs are very RAM demanding, these are usually recomended for dedicated folding boxen with at least a GIG of RAM, and currently only run on P4s. You must opt in for these WUs with the options WUs > 5mb and -advmethods both turned on.
Myth: My one computer can't make that much difference
Truth: Every computer helps more than you'd think. It would take the world's largest super computer hundreds of thousands of years to crunch all the folding work that needs done. But your computer can help take that load down. Just think if every computer on the planet was folding? We'd be done much quicker, we'd be that much closer to our goal...curing disease that claims thousands of lives each year. (someone might want to work on that one, it's the best I can explain it)
Additions from other people:
Myth: Running a CPU at 100% for weeks on end will "wear it out". (submitted by HTPC Rookie"
Truth: Explain to him that an electrical interface cannot wear out, it can only become damaged by extreme voltages, heat, or physical causes. I had a P3700MHz folding for 24/7, and it's still folding. Many people here have even older machines that still run. I think i'm near the top of the "I have an old crappy computer lying around" from the Mac "Lisa" in my garage that STILL RUNS. The only thing F@H can theoretically shorten is a drive lifespan, but considering how often the windows indexing service crawls the drive, if you disable that rarely-used feature, F@H will have no negative effect. (submitted by Shadowchild)
) with his permition to the folding effort. he isn't running it 24/7 but it will still do some work 
I'will also ad my ex-wife's rig (I've got her permission too
). it's a 3.2 prescott (I will OC it 
)Full folding ahead...