i'm pretty sure there isn't any problems with 2gb cards for the n73 but i don't have a n73 so don't hold me against that
the divx player for s60 plays avi files off the memory card because the n73, n80 etc dosen't have to processing power to decode on the fly like other s60 eg. n93, n95 so therefore they use divx player or smartmovie.
if you like the idea way to watch movies on your phone is to convert it to a mp4 format and downsize the screen size so the files is smaller. eg. a 700mb divx to a mp4 at 320x200 is about 200mb