where you're creating a pool that has only a single IP address, there's a shortcut. You can omit the ip nat pool command and instead tell the ip nat inside command to use the IP address of your serial (here second Ethernet )interface for translations. The result looks like this
! Define IP address translation (PAT) without using an address pool
ip nat inside source list 20 interface Ethernet 1overload
!
interface ethernet0
ip address 10.10.1.1 255.255.255.0
ip nat inside
!
interface ethernet1
ip address 172.168.1.1 255.255.255.0
ip nat outside
!
! Access list for our pool, which is used to select which IP addresses
! should be translated
access-list 20 permit 10.10.0.0 0.0.255.255