Tuning network performance

I manage a small network that has 13 workstations and 1 server, all running NT. Currently I have the network running TCP/IP. I just bought a Netgear 10/100 16 port switch, and am replacing 3 NICs that are still only capable of 10mbs. Now that I haveeverything set for 100Mbs connection, what can I do to tweak it to be very fast? Should I put all the workstations on NetBEui? How do I check for bottlenecks in my network? I want to improve performance. Any advice would be greatly appreciated.