Ok when I checked out your MOBO I found :
DDR400 (PC3200) Support
DDR400 (PC3200), the latest and fastest DDR memory standard, supports bandwidth up to 3.2GB/s to provide enhanced system performance.
It seems to me that your mobo will indeed support 2 Gb of 3200 RAM... It could be that your setup was off on the RAM.
Do you have the manual for your mobo ?
It will have the setup guide for your RAM.
I have 3 DIMM slots and have to skip the middle slot...
You may want to check that...