I don't use Vegas, but was looking at it for Video editing. What I discovered is that they apparently have discontinued Vegas Audio, and are now concentrating on Vegas VIDEO. The only difference is that video offers much more video capability while allowing all the same audio features.
Your choice of software might depend on what you're doing for backing tracks. Do you use MIDI instruments and sequencing? Are you into loops/resampling? What do you have for sound sources? Recording with mics, or direct from electronic instruments?
If you're doing little or no MIDI, Samplitude is a hard program to beat. It comes with several EFX, lots of processing tools, and although it is VERY deep it is also pretty friendly to get started. The more you learn, the deeper you can go. The sound quality of their mixing algorithm
beats Pro Tools according to comments by many people who use both.
One of the more popular all-in-one programs, at least for PC, is Sonar 2.0 - if you get the XL version, it comes with a few soft-synths and a couple of 64-bit mastering plug-ins.
If you decide on Vegas, spend the $30 extra and get Vegas Video 3.0 instead of Vegas Audio 2.0 - you get a full version newer and complete video editing with nothing lost in the Audio department. Here is one link for pricing:
http://soundstore.holdit.com/cgi-bin/cart.cgi?category=13&x=2
If you really only want the audio (with ONE video track) you can get Vegas Audio 2.0 for about $199 here
http://www.cdbm.com/shop/start.cgi
search on "vegas" (don't use the quotes in your search)
Hope this helps get you started, I'm pretty sure you'll have more questions - bring 'em on... Steve