I am mainly using Adium for instant messaging. However, due to limits in the file transfer capabilities of Adium, I sometimes need to switch to iChat, which involves taking my .Mac account in Adium offline, launching iChat, and going online there (I've set iChat not to go online at startup).
Here's a little AppleScript to automate this process. It basically toggles your .Mac/AIM account between Adium and iChat, so if your account in Adium is offline, it will take iChat offline and Adium online, and vice verca.
Note: If your account is an AIM account instead of .Mac, change Mac in the second line to AIM.
tell application "Adium"
set adiumAccount to ID of first account whose serviceID is "Mac"
set adiumOnline to online of account id adiumAccount
end tell
if adiumOnline then
tell application "Adium" to disconnect (account id adiumAccount)
tell application "iChat" to log in service "AIM"
else
tell application "Adium" to connect (account id adiumAccount)
tell application "iChat" to log out service "AIM"
end if
Save it into your user's ~/Library/Scripts folder, and invoke it via your preferred launcher to make this switching nearly instant.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060306170802462