I hate to suggest changing your workflow considering all you
asked was how to get your mic working, but...
I also have the same M-Audio Fast-Track box, and get awesome
results by recording to the open source sound editor 'Audacity.'
Actually, I prefer recording -outside- Captivate because I
find it's editing tools a bit limited.
The one or two times I recorded into Captivate (using another
mic), I ended up with a messed up (echos, drop-outs) audio track
after I did just a few minor edits.
My point is, rather than bang your head trying to get
Captivate to record, you might actually like things even better if
you record to another application and then import the sound clips.
FYI -- I haven't tried recording to Captivate via Fast-Track,
but I'll give that a whirl for you just to see what happens and
report back later.