$1000 HT System? Can it be done?

Was looking for recommendations on speakers, an amp, and probably a PCI card. I have a few months to shop around and wait for steals on audiogon. Most of my music-related audio needs come out of my computer(Mac G4), but I'd like decent surround for dvds and xbox and such.

An amp with a good headphone out would be very very nice, as I have some Sennheiser HD600s that could definitely benefit from a decent amp (Currently have a DIY Tube amp that's just a big headache)

Lastly, if anyone has any suggestions as to how to get great sound out of my Mac (New G4 desktop) and into an amp, that'd probably be an important component to include in the $1000 goal.

(Incidentally, I have a Yamaha YST-SW120 subwoofer. Not sure how it compares to others, but it does seem to do at least a decent job of filling in the bass of my current system, if not loudly.)

Thanks for any help you can give me!
-Gabe