iChat question

ok this is probably a stupid question but i just switched to Mac last weekend so i'm still getting used to it.

anyway what i'm wanting to know is, how do i sign off my ichat name? whenever i click the ichat icon in the Dock it automatically signs me into my @mac.com name and i want to sign on my AIM screen name. i know about Adium but i would really like to use iChat.

sorry if this question is stupid! i'm sure the answer is simple and i'm just overlooking something.

Have a look in:

iChat -> Preferences -> Accounts -> Account Information

And uncheck the option to have iChat automatically log you on when the program opens.