I think recording to a DAW on your PC using a USB interface is pretty straight forward these days. It's mainly about how many channels you can afford to record simultaneously. Remember every mic will need a cable, a stand, and a pre-amp. Some interfaces will have one or more pre-amps built in, but if the rest of the inputs are line inputs you'd need pre-amps on them
If you get an interface with 2 mic inputs (built in pre) you could do a decent job of recording the sound of your rehearsal with some clever micing. If you can afford one with 2 mic inputs and 2 line inputs, you could use the two mics for kick and snare, and then the two line inputs for a feed from the PA so no extra pre-amp required. Ideally you'd have a DI from bass, DI from guitar, kick, snare, and then you could take the 2 vocals out of the PA as one mono feed, but then you'd need 2 mic inputs and 3 line. Something like this: http://www.thomann.de/gb/steinberg_ur44.htm would be fine, but it's almost double the budget.
Beware of products like this: http://www.thomann.de/gb/alesis_multimix_4usb.htm which look perfect but only output a stereo mix to your PC rather than seperate channels