I just watched a hi-res Banjo-Kazooie comparison video on Gametrailers.com:
Game Trailers - Banjo-Kazooie N64/Xbox 360 Comparison hi-res
From what I can tell, the graphics are the same as the N64 version, except the Xbox 360 version runs in widescreen at a higher resolution with a higher frame rate. It looks very good, but it's not a complete makeover/remake like Conker: Live & Reloaded was.
I just wanted to clear up any confusion.
Joystiq - Rare will fix SDTV Banjo-Kazooie text issue
Joystiq - Rare to fix Banjo-Kazooie's text issues after all
Rare is planning to release a patch within the next 30 days to fix the text on standard-definition TVs. (Originally, Rare wasn't going to fix the problem.)