Trying to confirm that a Studio 1555 running Vista 64-bit can be upgraded from 4GB to 8GB.  Has two DDR2 slots occupied with pair of 200-pin 667MHz 2GB modules.

According to Dell's tech manuals this laptop will support 8GB.  But, I also have a Dimension 8300 desktop which was documented to support a max of 4GB, and it could only handle 3GB (couldn't boot with 4GB).

Has anyone had success running 8GB of memory in a Studio 1555?

Also, I typically see 800MHz DDR2 listed by vendors - does it matter, 667 vs. 800 MHz?

Thanks so much.