Yeah, try to gradually do it. Keep them seperated, seperate food, litter boxes, etc. ... keep them in different rooms too. Then maybe switch them in the rooms after a few days. Then maybe put them in ajoining rooms (with a door) for a small period of time, run a piece of string under the door and see if they will play with each other ... stuff like that, gradually introduce them. I will look and see if I can find any tips online and that to share with you too.
-B