upgrading compaq motherboard need help

Don't know if I can upgrade my compaq motherboard myself or if it's got windows info on it cuz of compaq. Here's my info so if you know anything and can help me that'd be great

Compaq 5423 US 5000 series

motherboard info
manufacture: compaq
model:0784h
chipset: intel i845d
southbridge: intel 82801BA (lCH2)
Intel Pentium 4 1.6

I have 2 512 pc2100 ddr sticks in it right now. I have 2 256 pc2100 ddr sticks I'd like to stick in but only have 2 memory slots, hence why I wanna upgrade.
I'd also like to get an amd instead of intel, or whatever is better. Any help would be awesome I have about $350 to spend. If I have to I can spend whatever on buying windows again if my motherboard isn't upgradable by myself.