Do you have the basic header & footer editor?
If not, it can be obtained at:
http://www.agoracart.com/addon_display.htm
How much different than the current layout do you want it?
This will probably determine if you really need to use the basic header/footer editor or if you should manually edit the store_header.inc & store_footer.inc files.
In the manager's store layout settings the "main body tag attributes" only handle the body tag of the store. In order to have the background image show up, you will need to put it in the same directory as the agora.cgi file.
HTH!
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God Bless!
Bonnie - AgoraCart Moderator
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