How can I make a backup of the 1.5 system in my eris before manually updating to 2.1?

[mjwamps]

Hi I am trying to make a backup file of the current operating system in my Verizon Eris. I am going to update it to the 2.1 ota from the zip file i downloaded and renamed earlier on google. I would really like to know an easy way to make a copy of my existing OS. does any one have any Ideas. Much thanks ahead of time to anyone who can figure this one out.
mj :reddroid: