Microsoft home networking is not that easy, but I think I have found the main problems. Now I have 2 pcs linked together via the HUB/Modem and a third linked to the main XP, via a wireless network and "bridged". All 3 pcs can surf the ADSL internet and each can exchange data and files via the main XP pc.
The main problems to solve are as follows:
Make sure you use the same Network name on all pcs "MSHOME"
Be careful to be consistent with your case.
Make sure the PC names are unique, and not the same name as your network.
Make sure you run the networking disk in each pc. If you don't they will not recognise each other. Your main pc should make this Networking disk for you. It does not come in the box nor on the disk with the drivers etc. This disk has to run on each pc on the network, then the pcs re-start and take some time to re-install the software on each pc.