redondo,
First off, you're ripping music from CDs, not burning them. You burn CDs when you're making them.
I found that 128kps is pretty common, but lately there's been a surge of 320kps MP3s out there. You're going to have to listen to 128 vs. 320 vs. a real CD to make the decision for yourself if you can tell the difference. I've heard artifacting at 128, and personally I rip at 192, but I've been thinking about moving to 256. 320 is overkill IMHO.
Mike