I want to record my songs. Nothing fancy, just:

Multiple vocal parts
Multiple guitar parts
Bass
Keyboards
Drums (I don't own a drumkit, I just like the possibility)

My budget is around $100, and I own a microphone with a standard jack. Also, both my guitar and my bass amps have recording output jacks. Finally, my stupid soundcard is broken and only gives me sound out of one channel. I'm assuming this is a problem, so what soundcard shout I get?

save a bit more and get this:
http://line6.com/toneport/
its what i use

Looks complicated.

Looks complicated.

No matter what method you end up using, it's gonna be complicated at first.

Welcome to the minefield that is home-recording. First of all, you're never going to get 100% brililant results on all those instruments for the money. If however, you're just looking to lay ideas down and have fun, then it should be great.

OK, as far as soundcards go, I'd check out:
- M-Audio Audiophile 2496
- E-MU 0404

Both of these will give you some decent sound, and if you end up taking the recording thing further, really help in the longer term.

In terms of actually recording the guitars, you've got a few options
- direct recording from the amp
I've never had any real success recording from the outputs of amps - what amps have you got?

- micing up amps
this is how the pros record guitars, however, given your limited budget, I'm not convinced that it would be your best option (see below)

- direct recording through amp modeller
I think the best option for recording guitars on a budget at hoime is the tone port/pod/v-amp etc (as sj_2150 suggested), if you can squeeze your budget to get something like this, you're likely to get the best results. The advantages of this rather than micing up your amps include:
- Better tone for the money (costs less than getting a mic that's really up to the job)
- No need to worry about room acoustics etc
- No need to worry about capturing household background noises (dog barking, dad sneezing, people knocking on the door)

The other thing you'll need if you don't already have one is some kind of sequencer (ie software that allows you to record multiple parts)

Hope this helps (having been through the process you're going through myself I know that it's more likely to confuse you than anything else!)

Okay, so I like that Line 6 thing, the $70 dollar one looks nice. I think I'll get that. As for soundcards, the E-MU 0404 is cheaper so I'd prefer to get that one, but what makes it special? And what sequencer software should I get? I already have Audicity, if that is what I need.

http://www.motu.com/products/motuaudio/828/

This is what I use. Excellent quality and pre-amps. Easy to use.
I connect it via Firewire to my Apple Macbook Pro, directly into Logic Pro, and use the internal mixer.
My guitar, I record with a SM-57 microphone (big surprise there...). Bass just directly into the DI of Motu828. Sometimes I also record the bass on a amp, with the SM-57.
I program the synths manually, because I'm not a good enough piano player to be tight enough.
Vocals and drums I usually record on cheap microphones, because the budget pretty much went away, after the microphones and Motu card.

SM57 - http://www.shure.com/ProAudio/Products/WiredMicrophones/us_pro_SM57-LC_content

Looks complicated.

this is easier if toneport looks complicated to you:

wait until you start doing some actual recording..
then EQing, effects and mixing.
and also, recording directly out of the outputs of your amps will sound like a pile of dogs being trampled to death.

Okay, so I like that Line 6 thing, the $70 dollar one looks nice. I think I'll get that. As for soundcards, the E-MU 0404 is cheaper so I'd prefer to get that one, but what makes it special? And what sequencer software should I get? I already have Audicity, if that is what I need.

The Toneport acts as an external soundcard, so no need for another there.
But I wouldn't recommend it if you're into heavy music.
I've got a Guitarport (basically the same thing without the micinput) and I haven't been able to create a good distortion in Gearbox. And this problem seems to be pretty common. I guess there is some way to get a heavy sound but it sure isn't easy. I even bought the metalpack which IMO was a pack of crap-presets.

Okay, so I like that Line 6 thing, the $70 dollar one looks nice. I think I'll get that. As for soundcards, the E-MU 0404 is cheaper so I'd prefer to get that one, but what makes it special? And what sequencer software should I get? I already have Audicity, if that is what I need.

The Toneport acts as an external soundcard, so no need for another there.
But I wouldn't recommend it if you're into heavy music.
I've got a Guitarport (basically the same thing without the micinput) and I haven't been able to create a good distortion in Gearbox. And this problem seems to be pretty common. I guess there is some way to get a heavy sound but it sure isn't easy. I even bought the metalpack which IMO was a pack of crap-presets.

it does take a while yeah but its not impossible