as recommended by a few people on this forum: BIAS sound soap is the best deal if all you need is software to clean up noisy recordings...
but maybe the problem can be fixed, what type of mic are you using... a computer usb one? or a computer' mic-input one?
i used to record with one mic with an acoustic and vocals, the key is to get the mic closer to your mouth than your guitar, soyou get a listenable balence between the 2, keep the input low, and keep sound checking before you record, put the input at a level where there is low background noise, and move the mic closer to your mouth, and see if you can get a satisfactory recording that way
(also, maybe the noise is coming from another windows audio channel, assuming youre using windows, check to make sure while youre recording that the line in volume is down if youre using the mic input..or viceversa...as well as other channels such as wave playback and cd playback are down or muted)
hope this info helps