As you aren't using mIRC, I can't guarantee that this will work..and the best place to ask about scripts for a client other than mIRC, is on that clients support system. Not all clients support scripting.
Addtionally, I found the script you're asking for in the mIRC help file, under /help on invite
This has been altered slightly from the one in the help file.
on *:INVITE:#:.join $chan | .timer 1 3 describe $chan appears in a puff of smoke!