Is it just for email/documents, or do you want any gaming done on it? $600 almost good enough for a mid-level gaming PC, assuming you have access to an OS already.
Base estimate~
HDD $100
2GRam $100
PSU $75
MOBO $100
CPU $150-200
VC would be up in the air though. And If you're spending more on a card, might as well toss in some more RAM to game...
Integrated sound is good enough for most non-audiophiles these days.
*edit* If you are tryibg to save money, a case can be had for $30-60. Late night.