I know absolutely nothing about Applescript, and I haven't played Starcraft in years, but I think that Warcraft 3 has pretty much the same hotkeys and battle.net setup. This is what would be needed to do what you want in Warcraft 3, and all it needs is keystrokes, no actual mouse needed, and I know there are programs in OS 9 capable of this, such as QuicKeys, should a script not pan out.
So Starcraft would launch as a startup item/whatever, and after a few seconds the "b" key would be input, taking you to battle.net login screen. The the login name can be automatically remembered, and I think if it is the password box is selected by default, so the script would just need type in the password, followed by the return key, which logs you onto bnet, and after a few seconds the "h" key, which would bring up the channel menu (with the channel name box already selected), and the script would type out the channel name, followed by the return key, bringing you to your channel. Remember, this is assuming that Starcraft and Warcraft use the same hotkeys within battle.net, which might be wrong.
Hopefully this might help someone here who actually does know how to write Applescripts (but might not know Starcraft) to help you out.
