Dude, did you really had any gamesaves on your box? I Have at least 13 gamesaves from action replay or xbmp, xbmc, mxm, etc, etc.. and never had a problem nor been banned. What that dude told you is highly unlikely, unless they have access to your gamesaves on E... but still that would be hard drive scanning.. something that hasn't been proved yet.
I really don't think they'll bann you for having AR gamesaves...
I would give them shit about it... Tell them you don't have AR, etc, etc,... to see if they give you a more satisfying answer.
As for eeprom and HD, you'll need both.
A new 100% virgin eeprom, and a new hard drive also 100 live virgin. Also a new gamertag will be required since yours is going to be flagged.
Check the "Marriage theory" thread, more info can be found within.
Sorry, I'm being a bit confusing... but I never heard that they'll bann you for having AR gamesaves in your xbox. Plus, the most common save to modify bios is 007, and other exploits...
Maybe you loged in with your modchip on, no?