My friend did this with his AIM a while back and so once I got the pearl I decided to try to set this up. It seemed complicated to set up and at first it worked great but it quickly started acting up and any time I signed into AIM it would freak out. Sometimes when I logged into google talk AIM contacts wouldnt show up. I just bagged the whole thing. Hopefully it'll work out for you but it's just all so hacked up and unreliable. Hopefully Google will set their service up to allow this soon enough and we won't have to resort to these things.
In my opinion you're better off just sticking with a multiclient or using separate apps. Good luck.