Just take it slow. I've done it a few times. I usually kept the cats separated for a while at first, and then occasionally had them swap rooms so they could smell each-other. Try to do that for a little while, maybe a few days, and then introduce them. They might hiss a little bit, but just let them go with it (unless they actually start fighting, in which case separate them). They will probably avoid each-other and occasionally hiss for the first few weeks, but as time goes on they'll get used to each-other.
How they get along really depends on their individual personalities. If your room-mates cat does start to bully your cat, then you can correct the problem by separating them or otherwise negatively reinforcing the bad behaviour. I have two cats now, and one was 3 when I got the younger one, and they have never been best friends but they live in general harmony and occasionally chase each-other and play.
