Roaming network bandwidth loss - ethernet hub?

If it's truly a hub, then yes, collisions are normal, and increase w/ more devices and usage. That's why switches have largely replaced hubs. Unlike hubs where devices must take turns (when more than one device attempts to use it, that creates a collision and the other device(s) back off for a period of time), a switch maintains dedicated connections between devices, so it's never shared, and thus throughput increases.

Now whether that’s truly the crux of your problem remains to be seen. Normally a hub works fine for a small number of users, certainly for ONE user. Where it fails is when you start to have many concurrent users, all waiting their turn at the hub. In that sense, it’s like wireless, it doesn’t scale well.

So then I really shouldn't be losing so much bandwidth if I just have a few systems plugged in to the hub? Is it possible that the hub is too slow? My internet should be ~20mb/s and the hub is 10base-t. When my computer is plugged directly into the hub and the only system, I'm still only gettings about 5mb/s of bandwidth.

Well if the hub is only 10Mbps (10BaseT), yeah, that's a bottleneck. And hubs are half-duplex, so they can’t send and receive at the same time. And you never get 100% efficiency either. So relying on a hub, particularly as old as that one sounds, is not a good idea. Time to move up to a switch. Even using an old router's 100Mbps switch would be an improvement. Standalone switches are pretty cheap too if you wait for a deal ($5-10).

Ok, I just replaced the hub with a D-Link DI-604 router, and disabled the DHCP server so it should be acting like a switch. I'm at about 3/4" the bandwidth I normally get, and it occasionally spikes to full bandwidth. Is there anything else I can do?