Topic: help configure nat!!

i need to know if i can implement NAT with dynamic ip address
Assigned to my WAN interface ?

this is the topology that i want to achieve:
the pc behind my LAN interface (vr0) will be received an ip address by DHCP server that will be configured on the alix board.

my WAN interface (vr1) will be defined as DHCP Client
and will be received an public ip address via the modem

the part that i can't figured out is the NAT from privet ip address from the pc's behind the lan interface to use the public ip address that assigned by the modem DHCP Server.

I'd appreciate your help asap and examples are more then welcome.
thanks in advance.