I can't really make any accurate statements on the video size that is possible and it probably also depends on a few other factors. However, as far as upload formats go, WMV is a pretty good and compatible choice. The files will be transcoded to Flash video on the server after the upload. MPEG-1 should work fine, too. I've also successfully uploaded a few AVI files (with Motion JPEG material in it). However, AVI is always somewhat tricky. As a container format it could hold a sheer endless variety of audio and video codecs, including some pretty exotic and special purpose codecs. Obviously, the software on the server that does the re-encoding and displaying of the file cannot possibly support all these codecs.