|It pretty much tells you what you can use at the link you posted for the motherboard:|
"Four 184-pin DDR SDRAM DIMM sockets
Supports dual channel (128-bit wide) memory interface
Supports up to 4GB system memory
Supports PC2100 (DDR266), PC2700 (DDR333) and PC3200 (DDR400) DDR SDRAM DIMM"
You have 4 DIMM slots & the system supports up to 4GB, so the max per slot is 1GB. The board supports dual channel mode so the RAM should be installed in matched pairs. And the 3 supported RAM speeds are listed.
If it was my system, I'd sh!tcan the 256MB PC2700 & replace it with 2 x 1GB PC3200. And I advise against buying RAM from eBay.