Which Account where ?
Apple IDs that can be used in iChat cannot be cancelled.
I have not tried but I am sure AIM offers a way to cancel/delete the account.
I am sure I have seen an option to delete a Google Mail account (which would disable Google Talk for iChat).
As for others I have not looked.
iMac 2.5Ghz 5i 2011 (Mountain Lion 10.8.3)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
Couple of iPhones and an iPad
"Limit the Logs to the Bits above Binary Images." No, Seriously