First off, how many computers do you have connected to your network and what exactly do you want to make faster? The outside Internet connection, file transfers, gaming, etc???
A switch is faster than a hub when you have multiple computers accessing the network at the same time (two transferring files while 2 game and one accesses the internet, for example), as it directs the network traffic only to the proper ports as opposed to sending the information to every port at the same time. It also allows full-duplex connections, which essentially bump the theoretical throughput to 200Mbps, which is great for large file transfers.
If you only have 2 computers, however, you will not notice any difference. Just remember: this will only change the speed of the internal network. It will not make your internet connection seem faster.
In order to make it 100Mbps, you need to have a 100Mb capable hub/switch, 100Mb capable network adapters in the computers, and CAT5 cable--unless you have VERY old CAT3 cable right now, your cable should be able to handle 100Mb.
If you are going to upgrade to 100Mbps, definitely get a switch. There is almost no difference in price, so you might as well just get the switch (check out the Linksys/Dlink 5 or 8 port switches--the 8 port models are available for less than $70).