Can I have two audio-lines out on my Macbook Pro?

I run the music for school fundraisers occasionally (they’re called “tech parties,” everyone games, etc). I’d like to be able to preview songs in firefox, or an audio program like iTunes, and only actually play music from one program.

I know there are programs to split your mac’s internal audio lines, so I can mute firefox but leave iTunes going (oh-so-useful for flash games :). But I’m not sure how to tackle this problem without using two computers, and an annoying file transfer situation in order to get music I was previewing on one machine to the other, and then play it.

I’d like to have two audio lines out, and manage which program plays to which line out.
a.) I don’t know how you have two lines out, or what hardware I’d need for that matter.
b.) Any good program recommendations for splitting the internal lines, routing specific programs to specific lines.