OK, so the badn im in (Metorical) has started to record some original tunes, catch is, we can only use the ****ty mic built in to our singer's computer (BTW we use electric drums), so if anyone has any ideas about how we could obtain better recordings, short of renting a studio or spending loads of money, it would be much appreciated. Check our band profile to hear the recording we've done. Any advice on microphone types, software etc. would be great.
Get an EMU 0404 USB ($220 Canadian) soundboard and a Shure SM57 microphone ($110 Canadian). Well either the EMU or an equivalent M-Audio would work as well. I just went through the same thing, did a pile of research and I purchased the above products. You may also want to make your own pop filter for the mic assuming you're recording vocals as well (search on how to make your own pop filter on google to make one for 5-7 bucks). The EMU comes with great software and works great in no time, easy to use Cakewalk Sonar LE.
Get a Line 6 tone port. You can run everything straight into the computer.

I use a Behringer V-AMP guitar pre-amp for recording guitar. Ive recorded vocals through it too.
I record with adobe audition. Its a simple program and Ive had some pretty good recordings come out.
m audio firewire 410 interface + apple macbook pro + native instruments guitar rig 2 + garageband

godly recording and low volume practice setup
He said he didnt have a lot of money to spend.

Ive heard that guitar rig doesnt sound good at all unless youve got an EMG 81. Revalver sounded like crap to me too. I was probably using it wrong anyways.
guitar rig is awesome if you have a good interface, a lot of ram, and know how to tweak the effects to your guitar and pickups.
My writing partner and I used onboard $5 sound cards on both of our PC's. He used a SM58 mic I believe and I used a Carvin CM87S LD Condenser mic. The recordings were amazing but he used to own a recording studio. Point is, if you know how to mix/master, with some decent mic's you can do a lot. We were both using Guitar Tracks Pro 3 at the time as well.

So with that, get a Large Diaphragm Condenser mic for vocals. If you want to mic the amps, try a Shure sm57 or sm58. I would consider trying a pod or v-amp though. Get's you more options for recording.