I have had several softmodded xboxs for years. Never tried enabling the HD modes as its my spare 28inch widescreen crt.
However you got to put a massive HDD in there. Its the whole point. Softmod, run XBMC and fill your drive full of emulators/roms and backups of your games. yes all the xbox games on my xbox are backed up orginals I own
XBMC is such an impressive piece of software. Keep all my videos and music on a NAS and its great for watching films in the bedroom.