Folding utilises memory speed more than the "amount", the "amount" of memory doesn't really matter, however the "speed" does.

Folding @ home loves 512MB + of fast memory.

In your case once you've reached 175MHz - the reason your getting instability is because your computer's PC2100 (133MHz/DDR266) is being overclocked To Far.

Personally i would sell ALL your memory and order 1GB GeIL Value PC3200 (£60 here in the UK).

check these links out:
http://www.chiefvalue.com/app/produc...-310&ATT=&CMP=
http://www.chiefvalue.com/app/produc...-309&ATT=&CMP=

Ideally if you REALLY want good memory, you want memory that can run @ very low timings, as this considerably increases memory bandwidth and efficiency of the CPU.

For example, Fred is getting 400-800 Point WU's, because:
1. He has 1GB of memory
2. It's Dual Channel (128Bit) (single = 64Bit)
3. it runs @ 2-2-2-5 Latency

This means he can run BIG WU's at a low latency, because Folding @ Home or anything thats purely CPU intensive is immediately effected by the speed / bandwidth of your memory, hence the faster your memory / latency the better.

Having 512MB (2x256MB) of 2-2-2-5 would get you more points than having 4GB Dual Channel CAS3 memory.

Ninja, download CPU-Z 1.27 and post a screeny of your SPD / CPU