The method Jeff mentioned can work well, but is very dependent on having the right room. If your room is too live, it'll sound like your player is at the end of the hallway, and you won't get any better isolation anyway, as the reflections are so strong. Actually, recording a singing guitarist will almost always bring the properties of the room forward, as the recording techniques tend to be a bit different to the isolated approach.
Another method that can work very well by itself, or as a complimentary configuration, is to use a single mic to capture everything. This won't work unless you have a great player, lots of time, experience, the right room, and great gear. Put up a quality LDC in omni around a metre from the player, stick on some good headphones, then take the time to move the mic around until you achieve the best possible tone and balance.
But one thing is certain, your player had better be very, very good if the results are to sound acceptable. Honestly, I've only worked with a few who have been good enough to pull this off. If your player isn't technically proficient, sensitive and innately musical, I'd be encouraging him to record vocals and guitar separately. No one practices anymore, it seems most are content with mediocrity, so I'd say (from my experience, at least) that there's a 90% chance this guy should be doing it separately :-) Of course, that very much depends where your working, past clients etc.
Have fun - it's a lot more fun recording bands and people all at once, you're going to love it!
post edited by jamescollins - 2014/01/16 01:19:10