Ah I'm home now and here's the info AnimalSavers gave me:

1. Separate completely for one week.
2. Second week, introduce the new cat to the old cat for around 10 to 20 minutes while one is in a carrier. (Use Fancy Feast or tuna in the carrier to get the cat to go in, so it doesn't emotionally strain the cat and has a positive association.)
3. Third week, introduce for same period while supervising the cats WITHOUT a carrier.
4. Fourth week, introduce for around 1 hour supervised.
5. 5th week, go for it.
There's more helpful tips online. READ ALL ABOUT IT.
If done willy-nilly, it can create PERMANENT problems and conflicts. Just imagine how you'd feel if someone just moved into your apartment. It might be an angel or perfect soul mate, but you'd be defensive, pissed off, and feel totally invaded. Ditto for cats.

and then she sent me this link: <http://spca.quiknet.com/handou_1.HTM#IntroNewCat>

All very helpful info