According th Intel, that Mobo supports up to 2GB of RAM.
Memory
Two 240-pin DDR2 SDRAM Dual Inline Memory Module (DIMM) sockets
Support for DDR2 667 or DDR2 533 MHz DIMMs
Support for up to 2 GB of system memory
http://www.intel.com/cd/channel/rese...ture/index.htm
XP 64Bit can cause more problems than it can solve.