SM57 + a good preamp will suit most guitar, vocal, and possibly bass guitar needs. It won't be the most optimal for some voices and bass sounds, but it will be a very usable and versatile setup. I recommend getting the full SM57 kit that comes with an XLR cable and stand - it's only like $10 extra. Later down the line, I would also recommend a decent compressor. They are very very very useful recording tools (if your preamp doesn't have one built in already). Here's a useful start on preamps:
http://www.sweetwater.com/insync/mic-preamp-buying-guide/
I'm assuming you are interesting in recording demos for yourself, right? If you ever want to play with drums, I highly recommend the Hydrogen drum machine (is it on Windows? I use it on my other computer which is Linux Mint). Hydrogen is very flexible, easy to use, has a large community with multiple drum sets readily available for free download, and best of all, is completely FREE.