Your system will have USB1 ports, and a hub cannot make them into anything else. If you get a hub, make sure you get a powered one.
Alternatively you could get a PCI card with up to four USB ports on it - in which case you could get a USB1 or a USB2 card. USB2 cards should come with drivers to enable them in earlier systems. Try and stay away from cards with Via USB chipsets., as they can be more problematical than other types.
You can get hubs and PCI USB cards at almost any computer shop, or any on-line store. I suggest you use a local shop (they're low cost from anywhere), and get some sort of "if it doesn't work can I exchange it" agreement.