IP Nat or forward

["Vernon A. Fort" <vfort@xxxxxxxxxxxxxxxxxxxxxxx>]

I need to NAT a VLAN or aliased interface to an internal address:

   192.168.90.1   ->   192.168.1.1

Basically a virtual network/address mapping.  The main reason is I need 
a IPSEC tunnel (openswan) connecting from a vender to an internal server 
but the ip address of our internal server is already used on their end.  
So, when they connect to 192.168.90.1, its redirected/forwarded/nat'd to 
the real internal address.

Can someone get me started.

Vernon