I would avoid Creative like a hawk right now, especially if you dont plan on gaming. Their Vista Drivers are absolute crap (My X-Fi Fatal1ty has never worked fully well in Vista and their customer service/forums are a joke).
As far as the difference between the Audigy2 and X-Fi. The X-Fi contains a much faster audio processor than the Audigy series. The audigies came out in like 2000 or so and the X-Fi's in like 2005 if IIRC. The audigy has support for later revisions of EAX and can do some more things involving digital encoding.
Since you are doing music/movies my suggestion would be looking into the HT-Omega Striker 7.1 or perhaps the Asus Xonar which is coming out soon. I think those are on par with an X-Fi but you havent specified which model X-fi you're looking into so its hard to say.