iChat 5.x.x works in Snow Leopard.
(Older versions also work in earlier OS versions)
iChat 4 and iChat 5 had a method of getting to a registration page for @mac.com names.
The iChat version no longer does this (but the registration page still exists)
In addition to this if you selected AIM then the option does not work now as AIM moved their Registration pages soon after Snow Leopard came out.
Keep the password to 16 characters or less (AIM server limit)
You cannot use an email that has already been used with or is an Apple ID.
You cannot exceed the 16 character limit here
You need an email for Confirmation and for Password recovery (You can use it again and again if you want to set up loads of names)
You can chose a Name or use an existing email.
iChat can also use Jabber IDs
Google Mail IDs can have Talk enabled in their Google Account settings and then it can be used in iChat
Facebook have a Chat option that needs enabling.
Both use Jabber servers and your ID with them is a Valid Jabber name.
There are lots of other Public Jabber servers.
Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"
iMac 2.5Ghz 5i 2011 (Lion 10.7.3)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
"Limit the Logs to the Bits above Binary Images." No, Seriously