Where to put code?

[freshJet]

OK, so I posted a thing about a Login PopUp a while ago, but now I'm stuck. I found this:

http://docs.jquery.com/UI/Dialog

What the hell do I do?

I want it to show after the user has logged in and is being redirected to the profile_main.tpl. What parts of the code on the jQuery tutorial do I need, and where do I put them? Also, I only want this to show once.