I'm using a Pod XT as an interface, with all the guitar-amp stuff turned off so it acts as a basic pre-amp. I don't see any reason why this can't be made to work acceptably.
OK, the reason this won't work very well is that mic preamps are different from guitar preamps. I think impedence has something to do with it. Anyway, you'll need a proper mic preamp. Avoid soundcard mic inputs at all cost, they are noisy as hell. Best thing to do might be start saving for a mixer, it'll come in very handy if you want to do serious home recording, and it'll have mic pre-amps. If you don't need that many channels you could get a standalone mic pre-amp which would probably be better quality than a pre-amp built into a mixer. It might also have EQ and compression as well.
Speaking of which, compression is practically a necessity when recording vocals. Not many people can sing at a completely even level, so you can end up with the volume right up in the mix but still not very clear at points. Compression will even this out. You'd be surprised how much of a difference it can make.
A better mic would also clearly be beneficial, but if you get the pre-amp sorted out you should still be able to get useable results with a cheap crappy mic (good enough for demos/just getting ideas down at least). As for mic placement, 6 inches does sound a bit far away; best to let the singer do whatever they're comfortable with, bearing in mind that the closer you get to the mic the bassier the signal gets.
You mentioned using a sock as a popper-stopper. Best way to do that is to bend a wire coat hanger into a circle and mount that between the vocalist and the mic (rather than just wrapping the sock round the mic). Also they usually recommend stockings for that, but thin enough socks should be ok. Anything too thick and I think you'd be getting rid of more than just pops...
Hope that's been of some help..
Dan
