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This might not sound worth it, and I've never tried it so I can't say for sure that it works. But I've heard that you get aim and make a profile. While still signed onto aim, sign on with gaim. then close aim. people will still be able to see your aim profile. if you sign off gaim you'll have to open aim and start again.
 
iChat 3 (in Tiger) will allow profiles. For now, use Adium, or just live without profiles like I am. Actually, I see no need for profiles anymore. Heh.
 
You have lots of options ... just Google for any of these:

* Adium
* iProfile (works with iChat to maintain a profile for you)
* Proteus (my personal favorite -- very Mac-like interface)
 
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