LAN speed seems slow

We have a small LAN (peer-to-peer). PC’s have 10/100 NIC’s, all connected to a 3Com SuperStack II Baseline Hub (model #3C16441) 10/100, which is then connected to the Internet via DSL. Why, then, does our LAN throughput always show a speed of 10Mbps? I’ve checked a few of the PC’s NIC configurations and see that they are either set at hardware default or auto select. Cabling and devices are all Cat5. I was just hired recently and given the task of figuring this out. Help!