Sound Production In The Orchestra Pit, Musical Theatre Options

[buzzplh]

I am musical director for a local theatre production. We don't have the budget to hire a full pit, and I was wanting to use synthesizers and MIDI to recreate the voices (we're talking about a dozen different voices).

I currently have a Mac iBook, I think it's a G3, and I have access to a Yamaha DX7. I don't have unlimited funds, but I do want this to sound good. What suggestions does anyone have for helping recreate band instruments through the computer?

Thanks in advance for your help.