Memory Fault

Hi all, I have installed W7 on an older model PC. The problem seem sto be with RAM, so I was wondering if it is maybe the OS or the motherboard. The motherboeard states the following:

Supports DDRII 533/400 up to 2GB Memory
Available with 2 DIMM slots supporting up to 2GB of DDRII 533 memory, GA-8VM800PMD-775 provides the highest performance platform with the high-bandwidth (4.2GB/s) mainstream DDRII memory solution.
Note: Use of a Double-Sided memory module (the single chip is 512 Mbit) is required if you wish to install a 1 GB memory module.

(specs from webpage)GIGABYTE - Product - Motherboard - Overview - GA-8VM800PMD-775

There are 2 1gig chips in, 1 speed 667 and the other 800. I have a problem with them working together, do you have any advice? It also sometimes shows 1.5gig and the 1gig.

I have scratched in the Bios aswell, but I dont see a higher speed than 266 in its memory settings

Please help,

Thanks all

533 divided by two is 266.5 the 533 is the double date rate (DDR)