Cubase LE is good, but Garageband, part of the iLife 06 suite is nice. I recorded a vocal trio to backing tracks and mixed it down to CD using only the effects provided in the program.
Like any software recording system, the more effects you add the more processing power you're using up, but garageband works real well.
I used the Presonus Firepod as an interface, worked fine. Any interface box will work.
If you're only doing a single audio input for a podcast, then Quicktime pro is good. It's not free, but for 30+ bucks it's worth the investment.
I've used a piece of Shareware.... D-SoundPro
you can google search it. Nice stand alone piece of software, does some amazing things with audio for a shareware product.
Hope this helps.
Jim