Replying to Exporting ( Adobe )

Hi, I'm making a movie with all last year's footage using Adobe Premiere and I was wondering if some of you were having the same problem. When I choose File / Export Timeline / Movie, I select Microsoft AVI, 640x480, DIVX Mpeg high motion, which seems to be a normal choice but when I open the result with Windows Media Player, Some parts of the movie are lagging and the same thing for the music, it's not fluid...

There must be a way to avoid that ( I don't think the fact that my computer is a pentium III 733 is the problem.)

Any help would be appreciate

Thanks a lot