well that's just the MOTHERBOARDS manufacturer saying it requires atleast 300w...that's not even counting the CPU, graphics card, hard drives, cd-rom, dvd-roms all that kind of stuff..but the way that CL25 is actually CL2.5 which means Cas Latency 2.5 ValueRam is usually at 3 so yours is pretty decent ram..thats what my 256 stick is actually...however...you are trying to mix two different speeds of RAM together which being socket 754 I don't know if that has something to do with it or what, but since one is PC3200 and the other is PC2100 you really need to get rid of that PC2100...try and sell it if you can for really cheap you'd be surprised what people will buy. That ram could be top of the line for someone who has a really old system looking for some cheap RAM. So yeah I would say that huge gap between PC2100 and PC3200 isn't good either.
Have you tried putting in JUST the 256mb stick? I would try that. That other memory is MUCH too slow especially with an AMD64 system man so just get rid of that alltogether and I'm sorry if throwing away 512mb stick of RAM seems like quite the Sacrifice, but in this instant it just won't due. Try out just that other piece of 256mb RAM and see what happens. Also there is a program called memtest86+ that you make as a bootable CD or Floppy that starts before windows to test the RAM, you should try each stick seperately to see if one or the other gets any errors. I can't stress enough though...it's pointless to leave in the PC2100....sell it off.....buy better......so unfortunately yes this means you're stuck with only 256mb but hey atleast you got PC3200 mines PC2700 at the moment
(Told you it'd be PC2100 geo
M&S doesn't ring a bell and I can't think of what company that might be. The only thing I could find is a site called M&S Computer at www.mscomputer.com
but I doubt that's the manufacturer of the RAM. Eitherway since it's not a well known brand then who really knows how good it is. So in the future you need to get a good brand like Corsair, Kingston, Geil, or OCZ are all good brands to consider.
Try and stick with CS2.5 RAM as that is pretty good especially considering your system unless you want top performance then you get high performance ram with CS2 and I don't even want to go into the other timings required in the full extent of ram vs ram so you should read up on it