Good idea, but you should think about upgrading. I might be wrong, but just recently I've heard, they've released the final version of XBMC that's supported for the XBox (unless some rogue agents update it). You'd be surprised how many things have been improved since the version you've used. Most changes are pretty subtle, but they're all pretty significant.
As long as you make sure the XBE file for the new XBMC is in the same folder as your current XBMC dash is located, the build will run. You'll just have to delete your old copy of XBMC on FTP and then FTP over the new build and reboot.
Just make sure you're not doing it during a thunderstorm, or on an outlet with 18 things plugged into it.
Also, make sure you have your eeprom saved to your PC as well. DON'T SKIP THIS STEP!!!!!!!!!!!!!!!!
As long as you have the eeprom from that machine backed up somewhere, I can walk you through setting up a hard drive from scratch if you mess anything up.