I've just built 3 computers in the last week. Just wait for the computer components to go on sale. I don't know if you guys have a "Fry's Electronics" where u live but try them. They sell cheap stuff. By cheap, I mean cheap pricewise, and quality. You gotta watch out what u buy though. I bought some ECS (I know they're crappy) motherboard/CPU combos for around $100.

Here's what I got in all:
2 ECS K7S5A boards w/ AMD 2100+ processors = $110 each
1 intel board w/ P4 2.4GHZ = $170 (GOOD DEAL)
40GB Maxtor HD = $50 each
bought 6 Kingston 512mb sticks (PC2700 DDR)= $40 each (supercheap)

Don't know why I'm listing all this, but it gives u an idea of what you can upgrade to. My recommendation is that you dump the celeron processor. They're crap. I think the front side bus only runs at 75MHz. Dont quote me though. I've had good experiences w/ both AMD thoroughbred and Pentium 4 processors. I prefer Pentium though.