Well funny but i am in a similar situation.
Just bought an Athlon xp 2800 and installed it in a Ga-7vaxp Giga-byte mobo.(via kt400 chip)
I still use my old pair of Kingston 512 Mb ddr Rams at 266.
my message in start screen says that it is a 2200 xp +.
Do i have to change the ram and go to DDR...