Can I use a 20-pin PSU in a 24-pin board?

Ok so I had a bunch of spare parts lying around so I decided to do a decent but cheap secondary build

Here's the stats:

Biostar Geforce 6100 mATX mobo
Athlon64 3000 1.8 GHz socket 939
XFX 6600GT 256MB
160GB IDE WD HDD, CD-RW. etc.
Cheap, but kinda cool looking Ultra mATX case

And to finish it off in the back of my closet I found an old Allied 350 watt psu, but it only has a 20-pin motherboard connector, but the motherboard has a 24-pin connector. I tried it and it does fit in, but I'm afraid to turn it on and I was wondering if it would work. So has anyone tried it? Also, I'm going to overclock this thing as far as it will go, will this limit me? I'm thinking that it might, but it's a fairly low power system so it might do OK. I really don't want to drop any cash on it since I've got a good system that I'm happy with. Any advice is appreciated.

Honestly I never mess around when it comes to power. Its a huge determining factor on the life of your components. With the price of power supplies from good companies as low as they are. Buy a new PS and save your self hours of trouble shooting with your OC.

be is right. The extra pins just supply additional current for the pre-existing voltages. If your old PS can provide enough +12V power, you'll be OK. The CPU and video card are the big users of +12V power.