Well, you could run win 95B or win98 on this PC and use win ICS to share the connection. Would need at least a direct PC to PC network connection. Don't need a hub unless you want to add more PC's, so all you need is a crossover network cable and one NIC for each PC.
Have a look at
www.practicallynetworked.com for ideas on how to share an internet connection with windows. Good stuff there.
A proxy server setup might be better though, than winICS, as you are sharing with XP, which might be touchy about the ICS from a 95b / 98 box. AnalogX Proxy should be fine for this (
www.analogx.com). And a firewall such as Zone Alarm may also run OK on that low spec PC, I think.
If you are adventurous, Linux might also be a goer, even using a special distro like Smoothwall to act a firewall / router. The beauty of Smoothwall is once you set it up, it's pretty easy to maintain. But it sorta depoends on hardware compatability, so check first (
www.smoothwall.org). And you may need 2 NIC's in the PC for Smoothwall - not sure.
If you want to set up a windows PC to run the share, I could help. For Linux, ask some of the linux gurus around the place.
Anyhow, whatever you do, have fun.
Cheers
Mick