Compaq deskpro ep-how much memory can i put inm running windows xp if i update b

i have an inherited compaq desk pro-ep/sb. I think it is a deskpro ep 6500-closest match.

It's a pentium 3 500 mhz, with intell 440 bx chipset and 686t2 bios. Last bios upgrade feb 99, would have tp update that?

alreadyu running xp. has 3 dimm slots, one holding a 256m memory board (kingston).

mother baord is 041hc, as#010233-001 for motherboard, which is sp# (spare part number) 118053.
serial number is 6941cjn4m017.
model number i think is p/n 166806-001, which corresponds to nothing i have found at the website or else where.

compaq p3 deskpro ep 6500 is closest match from compaq manuals at comapq bulliten (hp took over compaq).

sorry for the lack of eloquence...i've been working on this for hours with no final answer.

thanks-madeline