Memory Question

I have a question about AMD 64 bit processors.
This is a memory question. I have 2 machines basically the same.
The first one is a 754 built on a K2NEO 3200MHZ 512 of L2 cache with 2 gigs of 400mhz ram. The second one is 939 built on a K8NEO4 3500MHZ 512 of L2 cache with 2 gigs of 400mhz ram. Both running the same programs. The 754 says it runs out of memory. The 939 does not run out of memory. Both machines have Windows XP Pro.
Any ideals?