I don't know what you mean by backup / restore.. are you using a gui?
The best way to do these is to copy the config off the 2800 (I prefer to tftp), then edit the relevant parts of the text file, changing interface names, etc, and then paste this to the 2900. Once you gain experience you can just tftp the edited file up to the 2900 (of course you have to set up a temp address on it) and then reboot. You can also tftp to the running config but for some reason I always tftp to startup.
For the most part the 2900 is basically the same as the 2800. One gotcha I ran into is that some cards do not automatically show up on the 2900 (like they do on the 2800) until a command is entered to enable them. For example, for a channelized T1 card you have to enter the command such as "card T1 0 1" (Your entry may vary slightly depending upon the slot it is in.). Once this is done you can see the T1 controllers. You will need to configure the T1 controller with something like this:
controller T1 0/1/0
cablelength short 110
channel-group 0 timeslots 1-24
After you have done that, you will now see the serial interface associated with your T1.
(in this example, it would be s0/1/0:0
Once you get to this point with your serial ports set up, you can just edit the 2800 config and paste it to the 2900 after making the changes for interface names, etc
This card T1 think is something new with the 2900.
Having to configure the T1 controllers is because you have channelized T1 cards in your 2900 but you have the 1T1DSU card in the 2800. The 1T1DSU does not have the controller configuration requirement.
