Bro...
A mic pre-amp boosts the power thus the sound of your mic. If your recording a mic into a 4 track, a mic pre-amp will give your mic more power and sound but not necessarly make it sound like a better mic. I'm not nearly qualified to talk about this as I've been recording my own music for a year now regularly. I just switched to a computer and if your starting out, dont be tempted to go that route...have fun with the 4 track. If your recording electric, mic the amp, if your recording acoustic, put a mic about 6 - 10 inches away from the guitar aimed at the the 12th fret, away from the sound hole....record a song and listen to it and record it again with different positions. If you have two mics, I do one like that and the other comes over my shoulder down on the guitar. You can even put one away from the guitar and pick up the room....
What you'll want to do is use the search engine and type in key words on what your looking for.....mic pre amps.....mic techniques....etc....and just read. The folkd who post here have serious experience and REAL studios....this is an art and a science I never really appreciated until this past year. Now I think when you hear a ban on the radio your tempted to say "Wow...they sound good" What I now say is "Wow, who is their engineer or producer?" This end is just as much an art as the guys writing and performing our own stuff....
Anyway, check out the posts....and goto B&Noble and check out some of their recording selection...not too much but you can read chapters for free there...
If you want to get a pre, DONT just look at a Musicians Friend and pick one thats cheap that is hyped up in the print....I did that with a lot of stuff only to find posts here that recommend much better gear for the same cost and sometimes cheaper! As you learn more and you start wanting to expand your toys, as soon as you THINK you find the right piece....check it out here....chances are there is a post on it....and one more thing....dont post every time you want to know what people think about a pice of gear, a pre for example...I can bet
my HD-28 it will already have been posted.....
Good luck......play, record, listen, learn.....read......enjoy!
Michael