[notme23]

internet
|
| DHCP or static from ISP
| wan side
router
| lan side (192.168.1.x)
| DHCP out of router for internal network
|\
| \
| \
| 4PCs connected to router lan (192.168.1.x)
|
| ip range from router lan
| wan side (192.168.1.x)
NAS
| lan side (192.168.2.x)
| IP sharing enabled
| IP range different than router lan
|
4 PCs (192.168.2.x)

You may have issues with the PCs on the .1.x network accessing the PCs on the .2.x network and vise versa, but maybe not.

Another way to do it is to NOT use your NAS WAN port at all. Use only 3 ports on your nas for PCs and use the 4th port to connect to your routers LAN port. Turn off DHCP on the NAS and just use it like you would any other hub or switch. everyone is on the same IP range and everyone can access the internet.