You can't use a USB mic AND Fast Track at the same time(on a PC anyway). If vocals are your primary concern, then I suggest saving your money until you can get a much better interface, preamp AND microphone. Its tough to record serious vocals without spending for a more serious solution than any USB mic or M-Audio interface(Profire2626 being an exception). Even the new Mbox is (IMHO) a major improvement over the FTP
For the moment, what's you budget? Do you own any mics already? There are some surprisingly good "affordable" mics. The MXL V89(also available as the new CR89 for a higher price for the same mic in a new finish) is a shocker, and I just bought a new one from eBay for $218 with free shipping
). I own one already and want to try the pair as drum overheads(but its a very good vocal mic).