I have an XPS M1330, currently running 32-bit Windows 7. It currently has a 1GB and 2GB stick, both are DDR2 333. I recently received 2 sticks of 2GB DDR2 667 memory, which other people had success with on the same computer. The BIOS is at its most recent revision, A15. When I first inserted the new RAM, I was prompted to run tests on the RAM, which the computer then passed. When I attempted to boot to the OS, I was able to get into the desktop, but was greeted with a blue screen moments later. I reseated the RAM, only to be greeted with the blue sceen during the Welcome screen. For now, I have reseated the old memory, which allows me to still use the computer.
I assume that the problem is that I have 32-bit Windows, but I just want to double check that.
Windows 32-bit can't use more than 3.25GB, but it won't cause BSODs even if more memory is installed. The old modules should be running at 667 MHz (actually 333 MHz x 2 since they are DDR). If the system isn't stable when only the new modules are installed, then those modules are not compatible or there's an issue with one or both of them. Test them one at a time using Memtest86+ for a few passes.