Overdub
Hi, Booner.
When you use a computer to record, the overdubbing happens in the software. To overdub, follow the software directions. I use a US-122 and Cubasis. I just keep adding tracks or recording over old tracks. When you hit record, the sound that's already been recorded should show up at the US122 line outs. You'll also want to turn up the direct monitor knob so you can hear what you're adding. The new data will be show up on whichever track is active. I think you can highlight a section of a track in Cubasis and when you record it will replace just that section. I find it's easier to record a new track and cut and paste the new part into the track.
Hope this helps.
apl