I just build a machine not long ago (as did cditto, I think) and
I found that www.newegg.com
has the best prices - they also
ship fast, have good customer service, so you don't have to worry
about never getting your stuff.
RAM prices are dropping like grandma's saggy breastes's, so even
if you don't believe in it, you can get it cheap (i.e. PC2700 512MB
chip for ~$80!).
If you're not that interested in supremely high performance/overclocking,
I'd go with an Intel board (I got an 845GEBV, or something like
that) that has on board video/sound/lan card. You buy the board,
the processor, the RAM, a cheap hard drive, CD ROM drive and
a case, and you'll be at about ~$300.
good luck, keep posting questions if you got them...I got a lot
of help from this board.