My $.02.
Seems to me you are still wrestling with computer recording vs. 4 track. If by 4-track you mean tape, there are several issues to consider.
First of all editing on tape is destructive editing - meaning you tape over the original material. If you then decide the first take was better, it's gone. You can get around this by "bouncing" (recording the original material onto a new track and editing the new track), but each time you bounce on tape you degrade the signal. Also, you are limited to four tracks. You may think that's plenty, but if you decide to put in any harmony parts, or add a second guitar, you can quickly use up the 4-tracks (or you're back to bouncing).
Computer recording has many advantages. The number of tracks available (depending on the software) is virtually unlimited (64 to 128 typically). Secondly, copying a track (the digital equivalent of bouncing) involves no degradation, since you are just copying digits. Voila, you get an exact copy. You can also add software effects (reverb, delay, chorus, etc) and you can do this non-destructively - i.e., see what it sounds like without effecting or destroying the original material in the process.
Downsides? Steeper learning curve. Probably more $ to start. Also, there is the age old argument that analog is warmer than digital (this is where your pre-amps start to come into play).
Since you already have a computer, you can probably get a quite decent setup with a good sound card ($300 - $600), software ($100 - $300), a mixer - Mackie makes some good ones with decent preamps built in ($500 - $800). You could forego the mixer and just get a two-channel preamp (maybe $300). In addition you will also need mics and cables (which you need for the 4-track anyway).
You also need something to play the music back through. While you can use your computer speakers, you probably won't want to.
I guess I've talked myself full circle here, and it all depends on how serious you want to get. If you just want to record and hear yourself, get a radio shack mic, plug it into you existing sound card, and use Windows sound recorder to record. Investment will be about $10.00 and it will sound like s&%t.
