You create a nat-pool under the outgoing interface.
Then you create a class-map to match the traffic that needs to be nated.
Then you create a policy-map, match your class-map and select the nat-pool of the outgoing interface.
ie:
policy-map multi-match NAT1
class NAT1
nat dynamic 1 vlan 30
Finally, apply the policy-map to the incoming interface.
Gilles.