Well,
as far as mixers and monitors and all that, it mostly comes down to what you can afford...i wont go into specifics on brands or anything because its alot of ground and if you look around this site you should find most of it already is out there...
again, personally, as an amatuer at best, i would say the first thing to look at is a good sound card, most "pro audio" sound cards will record at higher sampling rates than your SB Audigy will and are designed specifically for recording audio, not just playback...depending on the # of inputs you need you can get a good quality M-Audio card for around $149 or so nowadays...i think that would be the best option to start with. if you get some of the higher range ones like the Delta 44, they come with breakout boxes so you dont really need a mixer...if you keep your SB card or get one of the 2 channel cards, you will likely need a mixer because you will need a way to plug your mics and guitar into the computer. Behringer makes decent cheap mixers, Mackie makes good mixers, just figure out what you want to record and when ( a track at a time vs. a whole band at once, etc.)
Your computer speakers will color the sound and that is a bad thing you will want to address down the road, but IMO your first priority should be getting the best audio you can IN to the computer before you start worrying about what comes out...
Stick around here, theres alot of people that know a whole lot more than i do on this stuff, (and may even correct things ive stated here so far ;-) ) and they have all been very helpful when its needed, so check out the site some more, you will find comments and opinions about most all the gear available from entry level to pro studio quality to help guide you.
good luck...