gxs,
I am sorry to be so confused but I just don't understand what you are trying to accomplish.....
Well not exactly like DMZ. I would just like to forward all data from a speciffic ip to a computer on a network.
Port forwarding will forward all connections (data?) to a specific port or range of ports from the external IP address to the internal IP address.
DMZ for all practical purposes makes the internal IP address become the external address. (any connection attempt (data?) on the external IP address will be made on the Internal address.)
If you are using your SME as a router and an internal fileserver only, DMZ would conceivably be possible with some fairly extensive surgery.
If SME is used for webserver or e-mail on the WWW the WAN IP address would no longer route to SME but would go to the DMZ'ed machine and would make the SME no longer available from the web.