Thanks for all the responses! I forgot that I needed an amp when I saw the nice deal on the Polk speakers. So factoring in the price of the amp will exceed my budget by a bit.
I'm reading up on the amps that ProtegeManiac recommended and they all sound like they'd do a great job. However, they're all more pricey than I'd like to spend. I'd like the find a good balance of decent speakers with decent amp/dac at $150 or so.
I'm starting to feel that this is too much to ask with such a small budget.
The deal on those Polks seems really good, so I wouldn't mind stretching my budget a little more for an amp if it means I can have some quality speakers.
As Sn0o mentioned, it would be nice to have something that would allow for me to expand my setup, even if just to include a subwoofer. However, that's not a priority for me now. I'll probably be using this setup for at least a year or two and I wouldn't mind upgrading to something else along the time. Also, I'm a "she", not a "he".
I still haven't made up my mind on a computer purchase yet, but I think I'm leaning towards an iMac now, so I think I'll be under my budget for the computer. This means I can probably increase my budget for audio gear (possibly up to $250/$300).
EDIT:
I forgot to add that I'd also consider active monitors. I just thought that at the price range I've set, there wouldn't be anything decent. If that's still true, then disregard this. Of course, I'd still like to find the best value for the money without having to really use up my entire budget, if possible.