Need to do motion graphics and titles for a HD kiosk, for an upcoming convention but I'm a bit lost as to which apps to get.

Can Apple's Motion render out to HD? What about After Effects?

I'm not familiar with either...

I also need to edit together SD and HD clips (up-res'd SD clips, most from DVD and DV tapes) with the titles and effects...

I'm on Mac, but I will spring for a WinPC if I need to.

Both Apple Motion and After Effects are capable of doing HD. Motion needs an incredibly powerful processor to run though.