Class C and Class B

We currently have a class C network at my present employer. Lately we’ve been hiring employees at a faster than ususal rate to the point that I have 15 free IP address to be accessed by the whole network. I’m on a Windows NT 4.0 server based network. With some devices using static addressing, my initial thought of changing IP address schemes to Class B from the server and DHCP clients would be easy. I had another thought of creating another network DHCP server on a newly purchased Win2K Server.
1)But if I do this would I also need a router/bridge/or Layer3 switch?
2)After the hardware is selected how do I get Class C to understand Class B is local, as far as keeping shared drives