Yea, it's a little tricky with the new 2800 series and non-ATM DS3 modules. The command you need to issue on the router is:
router(config)#card type <t3/e3> <slot#>
You'll need to pick whether the circuit is a T3(US) or E3(Europe), and then specify what slot it's in. After you issue the command, you will see a Serial interface created.
Hope this helps!