What do you mean by "it's not an .xbe"? Presumably you have downloaded a T3CH version of XBMC, have you made sure to make an XBOX ISO before burning it (using Qwix, Craxion or similar), and if so have you made sure that you only used the XBMC subfolder as source, not the entire archive as T3CH includes things for PC as well as the XBOX.
If this is all correct then I would reccommend the best thing to do is to try and get the XBOX networked to PC and FTP the folder over, as this is generally much more successful than burning to CD-RW (indeed, many XBOXes aren'table to read CD-RW, and only DVDs burned at a low speed).
