It will not work in theory nor in real life.
Right from the start:
>> If the SME server is 192.168.1.1; set the NetBSD 1.6.2 sever as 192.168.2.1.
They will not comunicate without router in between.
The main problem is that SME (as gateway) will respond to www, ssh and ftp (if enabled) itself.
You simply can not use the same port on given IP address for two computers.
You will need to either:
1.change SME's ports for those services to nonstandard and then unused standard ports (80, 22, 21) forward to internal NetBSD server.
2. use nonstandard ports for public access, forwarded to standard ports to internal NetBSD (public 88 > internal NetBSD's port 80 etc..)
3. Disable relevant services on SME and forward unused ports to internal NetBSD server. In this case it is not clear what you need this (SME) server for. e-mail and file sharing?