I playing a live gig and want to know if there is a way using my laptop to have live music play to audience and have separate click track play into my drummers headphones.
If you only want to send mono to the audience you could actually pan the music left and the click track right and send the left output to the monitor amp and the right output to your drummer's heaphones. Not elegant but it would work.
Alternatively connect an external USB or firewire audio interface with more than two audio outputs.
You can then direct a stereo pair to the monitoring for the audience and the click track out another pair, to your drummer's headphones.
There are a number of audio interfaces that can doing this, even some quite cheap audio cards for desktop PCs, but as you mentioned LAPTOP then an external interface would be the way to go.
Check out Edirol, ProTools MBox 2 Pro(I'd probably use their software for this as well but the interfaces do work with Vegas), ESI U46, Hercules ESP1010, MaxVibes U46DJMK2 to mention a small collection.