>Where I work, when I had the chance to influence the design of the network, I made sure I got switches (one 10Mbit and the other a 10/100Mbit - both 3COM). Because we were going to take a little while to upgrade all the computers placing a switch in the loop helped everyone. The old system had a 10-base-2 (Ed R - proper nomenclature?) and so it slowed everyone down to the lower speed.
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Actally, it's 10BaseT and 100BaseT (or TX, or a couple of other Fast EtherNet implementations), on UTP (Unshielded Twisted Pair) cabling. 10BaseT requires Cat3 cabling or better, 100BaseTX requires Cat5 or better. There's a different designation for the STP (Shielded Twisted Pair) cable plant. 10Base2 is Thin EtherNet, aka CheaperNet, on RG58 coax. 10Base5 is Thick EtherNet.