Isolation is the Key

The main reason for a 2 room setup is being isolated from the direct sound of the performance as it's being played. What you are most concerned with is the sound that's coming through the microphone. This way you can hear any noise or distortion in the sound as well as beginning to shape what the final sound of this performance will be. When you are isolated from direct ambient sounds of a drum kit you can make better decisions about where to place microphones apply some compression to even out the volume of the kick and snare drum and generally shape the sound of the kit as you record these sounds. This is very important for those operating demo studios where time is money. This also helps ensure that a great performance won't have to be scrapped because of a technical problem that results from you not being able to hear a problem in the first place. This of course is less critical if you are recording your self or your own band and you have unlimited time for re-takes. If you are a hired gun recordist you should always strive for the situation where you are always waiting on the client, but the client is never waiting on you.

If you only have a one room setup, the best way to compensate is to develop you own standard way of getting a fairly neutral sound recorded that you can play with in the mix. It's best to record dry sounds and use plugins or patch in outboard gear to add effects afterwards. You may also want to master the art of re-amping your guitars. This involves recording a plain jane guitar signal into your recording rig and then routing that signal back out to an amplifier with a microphone on it. There are also many plugins that allow you to make great sounds from an un-effected dry direct guitar. I personally always seem to prefer the sound of an actual microphone on a real guitar amp!