I would recommend you do not keep installing different distro to fix the problems you are having. Spend some time, read the documents for Samba, ask questions here.

One other suggestion I have, install LinNeighborhood on your linux machine. It is graphical, allows you to scan the network and mount remote shares.

Happily, my broadband link is only 512k so it will take a day to get another distro. In that time I think I've finally bottomed the problem. This might be old news, but just in case here goes:

I made not further changes to the Linux system other than creating another shared folder. This didn't work either! Shut down both machines, and by chance started the Linux one to use the internet. I then started the XP machine to copy a disk. Whilst they were running I thought I would check again. The network was running fine, with all shares visible. It turns out that the Linux (server) has to be fully up and running before the XP machine. Interestingly, a restart on either machine will still not allow the machines to communicate. It has to be a shut down. I can only assume it is something to do with the way my router allocates ip addresses or some other DHCP black magic.