You should be able to find the stock ROM somewhere (probably on xda) and apply it to your phone, then upgrade from that. Just make sure you do a backup in case something gets messed up.

 

What specifically needs to be backed up and whats the easiest method for for performing the backup?

 

need to do a nandroid backup...head over to xda and look into the nexus one development sub-forum.

not to be an a$$ but you probably shouldnt be flashing roms without some knowledge of what/how to backup...you could very easily end up with a 500$ paperweight...

 

I couldn't agree more. Notice I said I haven't flashed mine yet and that's precisely why I'm asking here. BTW, have you seen any mention of a backup in any of the hundreds of posts with all of the cookbook instructions for manually flashing froyo? I haven't even seen it causally mentioned anywhere.

Well, for whatever its worth, I guess the average user is also going to flash 2.2 via the OTA upgrade and they probably wont be given backup instructions for that either.