Ouch...lol. I would say a Mac Pro with maybe minimum 12GB of ram. Maybe a hexa core machine 3.33GHZ seems to be the best bang for the buck from what I've been hearing. With at least a 64 bit video editor that would allow you to use more then 4GB of ram. iMovie is only 32 bit. Yeah you could do it on much less, but considering the amount of shows and length, render time would be quite lengthy on a lesser machine.

But hey, thats just me. I would do your research and talk with some other video editors to see what they think.

Curious, how many shows and are they 1-2 hours a piece or all together? How many times a week?