Auto-suggest usernames function - where is it?

[James Birkett]

I'm trying to make a twitter/facebook-style username hyperlink for my shoutbox and I wanted to implement vBulletin 4's suggest usernames feature (that it uses for PMs and such).

The way my modification would work is:
User types "@" then the username, as the user begins typing the username it would suggest users, based on vBulletin's suggest feature and the letters typed (obviously if you type 'A' it would suggest all of 'A'.

My question: where is the function that suggests usernames?

Thanks in advance.