Can someone explaine something to me?
Okay I have a sure SM58 Mic and when I run it into my computer it sounds lame. When I put a little MP3 recorder that cost 6 pounds in front of my 4 x 12 it sounds SO much better - how the amp really sounds in the room.
The mic will require a certain level of power that your computer may not be outputting properly, especially if it's onboard sound. I have to use a headphone amp with my simple headphones to get good sound if I use my onboard sound (which I sure as hell don't - I use my M-Audio FireWire410). You can buy mic pre-amps for under $50, though. That will work wonders if your system isn't doing it for you.
As for the original poster if you want a proper interface for instrument recording do not get a gaming card like the Auzentech or creative. You need something with multiple inputs/outputs, midi, compatibility with programs etc. Like suggested earlier M-Audio has a ton of external interfaces that work with either FireWire or USB. Keep in mind M-Audio has the worst driver development team in history so check drivers support and what not for your computer before you buy. Also, M-Audio FireWire products aren't hot pluggable so that's also a downer.
I personally suggest you look into getting a PreSonus FireBox used off of 'the Bay' or what-not. It's almost exactly like the FireWire410 from M-Audio but is also hot pluggable firewire and has good drivers. People are really recommending this box a lot lately. Even if you can't afford one, or find one used, save up. The great thing about interfaces, unlike gaming sound cards, is that their technology doesn't really get old. You can have an interface for years and years. Like the Firewire410 I have - it's been around for years yet is still a top seller. So, buying one that has everything you need and is a quality product is a very worthy investment into a hobby that may become something a lot bigger than you originally though it would.
Oh, and as for needing a firewire port, you can buy internal firewire controller cards of 'the bay' for mere dollars. Hell, I recently bought one for THREE dollars. Hehe, the shipping was more than the friggin' card was.
A suggestion for an external USB interface under $200 new (try finding better ones used first), though ('cause that was your real question) would be: M-Audio Fast Track Pro or the E-Mu 0404. And for the same but firewire check out the PreSonus Inspire.
Still, save for, or buy used, a PreSonus FireBox. You'll be glad you did.