How Much RAM Do You Really Need?

I am a little confused as to what ram would work better with the Asus P5KPL-CM motherboard running intel E5200 CPU. I will not be gaming.I know I can use up to 3.5 Gbs of ram on my Windows XP 32 bit OS.The question is which would perform better> 2x1Gb ddr2-800 pc2 6400 or ddr2-667 pc2-5300?

I use a Mac and a windows computer from IBM. I use the mac most of the time... it has 768 megabytes of ram.
The Mac is a powerbook G4.
Applications do crash but I like to do things quickly so that's why. With the IBM (Netvista), I don't use it that much, but sometimes I control it through RDC. The "Netvista" has 1 Gigabyte of ram.
I don't really mind about the computers and the ram-I just care about that I can use them and that they don't crash each time I play a game.
From someone, who is learning applescript.

I've got 12 gB of RAM and I still experience slowdowns. Today it was due to numerous programs reading my hard drive - and even the RAID 5 array didn't help.

Performance is achieved by striking a good balance between RAM, CPU, Hard disks, and the mobo.

my 256mb ram pc is working surprisingly fast.it take 2 minutes to load while my laptop got 2 gb ram and takes like 5mins to start up.my 256mb ram system has been (like you were saying) balanced to do tasks throughout the system that are necessary only and working amazingly well.