I don't know anything about vimeo, but perhaps I can give you some background that might help you solve the problem...
vimeo has a
help/compression web page. The format options are fairly limited. H.264 at 640x480 or 1280x720. It also says "1440x1080 will not be widescreen on vimeo."
I assume you have seen other widescreen videos on vimeo?
I assume your converted file plays OK in Windows Media Player before you upload it?
Yo might try using
SUPER (FREE!!!) to convert the file. I don't know if it will help, but it's a way for you to try a different encoder. (Import your DVD into Video Studio, save it as MPEG-2, and then use SUPER to convert the MPEG-2 to H.264.)
Most video file formats have a field in the file header that specifies the aspect ratio. So in theory, this shouldn't happen (but it does). If something's not displaying properly, it could be a problem with the video file header (caused by the encoder), or the decoder software is defective, or simply can't handle the particular aspect ratio for that particular format... Maybe vimeo only displays square pixels.
Note that most video formats
can use non-square pixels, so the pixel ratio (resolution) is often different from the aspect ratio. For example, both 4x3 and 16x9 DVDs have the same pixel resolution (720x480 for NTSC and 720x576 for PAL). Both regular and widescreen DVDs use non-square pixels.