Some NICS and HUBs don't like talking to each other if they're forced to go full duplex and 100Mbs. In theory, you don't need the full duplex enabled except if you're copying files from A to B and B to A at the same time; It's usually this that screws it up. Apparently it's something to do with the layers and translation when IP's go to MAC address and hardware handshaking... IT all depends on your hub and NICs as well - what make are they?
Lots of hub manufacturers trick the consumer into thinking that a 10/100 hub is full duplex, but when in reality it's just tricky advertising to mean that it will switch from 10mbps to 100mbps. Your hub might say it's dual speed, but that only means that it supports Ethernet/Fastethernet (10/100). Dual speed and dual duplex are two different things.