if you are not connecting to the internet, then you can stay with the 192.168 range of IP's:
What I'd do:
192.168.0.0 --> "network" IP address (reserved)
192.168.0.1 --> "gateway" IP address (not reserved, but leave it for future use.)
192.168.0.2 --> linux server
192.168.0.20 to 192.168.0.253 --> use for windows PCs.
192.168.0.254 --> "gateway" IP address (not reserved, but leave it for future use.)
192.168.0.255 --> "broadcast" address (reserved).
This way, you keep some IP's (3 to 19) for adding more servers and knowing they are servers, and you keep all PC's at the range 20 to 253.
If you get dhcp to work on the linux server, you can let it hadle assignment of IP address for PC's automagically for the range you provide (i.e. 20 to 253)
You can set the mask on all machines to 255.255.255.0
NOTE: If you use 192.168.3.X instead of 192.168.0.X for the machines, and a mask of 255.255.255.0, then note that using a 192.168.0.X will not mix well with 192.168.3.X IPs
Consider the third 255 as a constraint for the IP to mix when the third element of the IP changes.