The WPN Gaim/Pidgin plugin should work just fine on the PS3 if you want color.
As the others have said there are only a few Linux chatclients available.
I dont know of any of hand with source code but all you need is the code, the makefile, config script, and the GNU build tools.
I'm sorry i never responded when you posted i was out of town and never saw this in my "unread posts" thing when i returned.
INCORRECT! WINE does work on PowerPC, it just includes an extra program to emulate the x86, but is not a full VM. I haven't a clue where to get it, but it does indeed exist.
This is unlikely to work. Remember the Ps3 uses an IBM/Sony CELL processor. While loosely based on PPC its not 100% PPC otherwise it would be the IBM PPC G6 or G7/(+>7).
As stripes said Boches could work.
Its tricky to configure but there are gigs of documentation on it.