I had odd problems running 8GB in this machine, and have reverted back to 4GB without these problems. This PC has a Pentium Dual E2180 processor, 4 RAM slots, and BIOS is 1.0.18. The original OS is Vista-32. Here's what happened:
At 4GB: Fresh install of Windows 7 64-bit - no problems.
Installed 8GB RAM: No obvious problems (8GB indicated in BIOS and Windows 7). However, my wife (her computer) began installing her previous Big Fish games and encountered errors with most of them ("failed to write to memory xxx"). Everything else appeared to work normally, although the PC seemed a bit slow. After working with Big Fish support, no solution was found.
Fresh install Vista-64: Just before its first restart, error window appeared "Windows setup could not configure Windows to run on this computer's hardware".
Fresh install Vista-32: Same Windows setup error as above.
Fresh install XP-32: Same Windows setup error as above.
Installed 4GB RAM: Fresh install XP-32 normally. Big Fish games installed without problems.
Even though the problems occurred only with Big Fish games (other applications installed without error), I can only conclude that there was some addressing issue with the memory controller/CPU. I also noticed that copying files from a USB memory stick took about twice as long as normal.
At the moment, the 4GB PC is running well with XP, and it would run OK with Vista or Windows 7, 32 or 64-bit OS. Windows install objected to something with the 8GB motherboard, although Windows didn't object to the 4->8GB upgrade after Windows was installed at 4GB. Funny, that.