Try this:
Mic into pre-amp, pre-amp into compressor, compressor into desk (or sound-card or whatever. If you have insert points on your desk you can put the compressor on an insert on the channel you have the vocals on). Remember you can't undo the compression once it's recorded so you might want to be less than radical with your compressor settings. Try a ratio of 4:1. You'll have to get your singer in and play around with threshold and make-up levels to get some settings that give a good level. Personally, for recording vocals I wouldn't do what neil suggests - actually a don't really use compressors like that at all, but some people do like mixing up their drums that way. Anyway you may want to compress the vocals again when you come to mix-down so that they cut through the mix a bit better, but you can afford to mess around more then.
KasioRoks