"Which mic should I buy, why can't I buy it at Radio Shack, and which way do I point it?"
The 'Radio Shack' section of that quote (from the description of this forum) is important. Their microphones (well, most everything they sell) is widely reputed to be crapola.
Recording good-sounding vocals is complicated. Here's the deal--you need a professional mic (more on that later). You won't be able to plug it directly into your computer's sound card, because you need a mic preamp, which amplifies the microphone's output to line level. There may be a little mic preamp on your soundcard, but it'll sound terrible. So what you really need is a better mic plus a nice pre-amp. If vocals are the only thing you're worrying about at the moment, invest in a nice preamp. I hear that a not-so-nice mic through a good preamp will sound much better than a nice mic through a bad preamp. Unfortunately, I don't know much about what's available for outboard pres, so somebody else will have to help you with that. As far as microphones go, it depends on your budget. A Shure SM-58 would be pretty decent, but they're mainly for live use. Vocals on CDs are almost always recorded with condensor mics (the 58 is a dynamic). I don't understand the difference in the way they work well enough to articulate it, but the bottom line is condensors are much more sensitive and pick up more high end signal. They also require a power source, whereas dynamic mics do not. This is called phantom power, and you'll find it on any mic pre or mixer worth its salt. It used to be that a good condensor was hard to come by on the cheap, but these days some good low-cost units are available, among them the Marshall V67 and the Studio Projects C1 (
www.mxlmics.com, www.studioprojectsusa.com). I've never used either unit, so I can't exactly recommend them, but they have good reputations around here.
On the other hand, if you think you'll want to record from several mics at once (like recording a drumkit for instance), it becomes to expensive for the likes of us to buy a bunch of seperate nice pres, so you need a smallish mixer. That's a whole nother can of worms. But anyway, I hope this info gets you started.