Hi,
The first thing to check is whether Windows XP has bridged your network
connection. to chekc this;
1. Open network connections
2. Check that you have a LAN connection and that there is NOT a
connection that has been bridged. (This is when two network connections
are joined together, will appear as a bridge icon).
3. If a connection has been bridged then right-hand click on the bridge
connection and choose 'disable'. Then delete it.
If this does not work then please try the following on all of the
machines:
1. Open the properties for your LAN connection
2. Remove all of the protocols, services and components in the box on
the properties page (you will not be able to remove TCP/IP in XP).
3. Then install the following:
-Client for Microsoft Networks
-File & Printer sharing....
(If the top alone don't fix the problem try adding the bottom 2 as well
below

-NWLink NetBIOS
-NWLink IPX\SPX...
4. Restart the computer (try this on all machines)
If that doesn't work then please try the following:
Check to see if Simple File Sharing (Control Panel - Folder Options -
View - Advanced settings) is enabled or disabled.
For XP Home with Simple File Sharing enabled, make sure that the Guest
account is enabled, thru Local User Manager (Start - Run -
"lusrmgr.msc"), on each computer. Do any of the computers have a
software firewall (ICF or third party)? If so, you need to configure
them for file sharing, by opening ports TCP 139, 445 and UDP 137, 138,
445, and / or by identifying the other computers as present in the
Local (Trusted) zone. Firewall configurations are a very common cause
of (network) browser, and file sharing, problems.
Let me know how you get on, Luke.