many soundcards have issues with full duplex performance..
I haven't been able to get around it with my Via based AC'97 card. (Yes, I know it's old).
It's one of the drawbacks I can see,
meaning you can't record and play at the sametime.
On the other hand, if anyone knows how to get around this, lemmeknow
Audacity and Ardour both look like they'll work great. I used Audacity for a while, with pretty good results running two soundcards -- one for playing, one for recording.