So I wanted to get a mic to record guitar with, but then I found out that I also need a mic preamp and an analog to digital converter (i think?).

I was looking at the Shure sm57 since it seems to be a popular choice for guitar recording, so I guess Im asking what else do I need to record guitar, and what is the best I can get for around 100$ (minus the mic), in terms of preamps and whatever else I need

Thanks for the pleh!
You only need a good interface (presonus audiobox) and a good recording software (Reaper)
That looks about right, is a firewire interface particularly better than a usb? also, how much does the quality of the interface affect the overall recording? Should I spend more on the mic or the box?

read a few stickies in the recordings and riffs forum, do a quick search and then make a thread if you still have questions. lots of info and you should be able to answer a lot of your questions with minimal searching.