Well, I googled the T2672 and you do indeed have the right ram PC2700 DDR333. That MOBO supports up to 2G only 2 slots.
I'm not sure why you are trying to run a 512/slot1 and a 256/slot2 though. If you run (2) 256 in slot1/2 you are taking advantage of the rams Dual Channel capabilities. If you run the 512/256 you are not. They need to be two identical pairs.
As far as not being able to boot with the 512 installed, I would assume that this is a issue with the BIOS. WHat BIO'S is it? AWARD? If i were you, if you know how, i'd try installing new drivers for that MOBO, and possibly flashing the BIOS's. Although you should make a back-up of the current BIOS. And make sure you have the right upgrade for the BIOS.
Google it... You'll find plenty of updates...