To get the best sound quality for under $1000, you should plan on playing music from your mac, not iPod. With the iPod your stuck with the internal DAC which isn't the best. With the Powerbook you can use either the optical or USB out to get a direct digital signal.
So you'll need a DAC, amp, and speakers.
You could take care of the DAC and amp with the Harman Kardon 3490 receiver which is powerful enough to drive any speakers, and has an internal DAC - which is rare with stereo amplifiers. You can get them refurbished direct from Harman Kardon for about $250 here: Harmon Kardon Ebay Store
So that leaves $750 for speakers. There are a lot of different ways to go here, but I would suggest either a nice pair of bookshelf speakers, or a less expensive set of speakers and a cheap sub if you want to fill out the low end. Definitely look for used to get more for your money.
Some to look at would be Ascend Sierras, Era D5, Paradigm, Energy, NHT, PSB, KEF....really a lot to research and choose from.
If you want a sub, I would look for a used Energy sub. Even their low end subs do surprisingly well with music. I got a $75 ESW-8 and it's actually pretty decent.
I hope that helps. Is that the kind of info you're looking for?
Ryan
