100 = 100 Mbit/s (as opposed to a 10 megabit hub, which eest suggested; 10 MBit/s is pretty much obsolete now, unless you have a 10 Mbit/s ethernet card, which would pretty much have to be manufactured in the 80s

Base = Baseband--That is, it's a non-multiplexed, digital medium

T = Twisted Pair cabling (As opposed to coax, which was used in the older 10Base2 and 10Base5 technologies)

X refers to the full-duplexing nature of the technology; There is such thing as 100BaseT which achieves the 100 MBit's data transfer rate, but 100BaseT is a half-duplex technology, whereas 100BaseTX is a full-duplexing technology; Basically, it means that with 100BaseT, while you upload, you can't download--transmission can go either way. 100BaseTX can effectively double the throughput by uploading and downloading at the same time.

Mind you, with conventional broadband internet, 10BaseT will do just fine, since you're only transmitting over the wide area connection (read: the internet) at a maximum throughput of 1.544 MBits/s (assuming aDSL), but 10 vs 100 makes a *huge* difference on the local area network. With 100BaseTX, working over the LAN is almost as fast as doing everything on the local machine.

Of course, with all twisted-pair networks, there's the maximum cable segment to be wary of--You can't go more than 185 m of cable without a repeater--such as a hub--but who the devil needs THAT much network cable inside of their house?

Also, 100BaseTX, unlike 100BaseT, actually *requires* Cat5 patch cable, but you'll probably be using Cat5 or even Cat5e anyways. Cat5 is what you get if you just go into your local Gaydio Shack or FutileShop and ask for network cable.