first off are they hubs or switches? The auction says they are hubs, while some quick googling says they are switches (edit:thye are hubs, my bad). there is a big difference between the 2, hubs transfer data to all the ports, while switches transfer it to only its intended recipient. Hubs can get congested quickly when you have many ports, switches would provide better ping in the long run, and have less collisions, but you should be fine with hubs for now. With hubs though, the theoretical limit is 100mbit total, as all traffic is broadcasted everywhere, yet with switches the traffic only goes to its intended port, so you have a theoritical limit of 100mbit a port (200mb full duplex on a 10/100 switch, assuming there is no backbone limit, cause we don't need to worry about that for now) See below for some more about bandwith and lan games
Contrary to popular belief, gigE (gigabit) is not needed for gaming, games don't use that much bandwith (we're talking less than a half a megabit a client.) gigE is useful right now for connecting fileservers to a core switch, and linking switches togeather (covered with those 3coms by a propriotary interface already) and for networks with lots of high bandwith apps going at one, like file sharing, distributed rendering, video editing (over a san/nas), etc.
The average lan gamer is not going to notice a difference between gigE and 100mb ethernet, unless you have a MASSIVE leech fest, in which case (with gigE) you might run into hard disk limitation (not sure on that, but you get my point)
wow that was long, hope it helps, IM if you have any questions