I'm going to assume you 'bricked' your 6700 the same way i 'bricked' mine. Are you seeing the first boot screen and then nothing?
If so, I did it by trying to flash a ROM using Windows Vista and did not have everything setup properly. Using a XP machine allowed me to flash the stock ROM without any problem.
If this story sounds familar, the following post by PDAPhoneJunkie should help:
http://forum.ppcgeeks.com/showthread.php?t=49837