I pretty much already concluded it was a permission issue on the XP machine.
Running the network setup wizard is the best way to fix this problem. Running the network set up wizard is standard procedure to enable sharing from the XP machine. Have you done that yet Ronnie?
Do you plan on using workgroup or public for file sharing?
If you are using an Anti Virus program you should disable it or uninstall it if it still doesn't work.
You should not have to have the same user name on both machines but it sometimes helps when there are problems although it shouldn't matter if you aren't using passwords. Both machines need to use a different machine name but can use the same user name.
Make sure these settings are all set correctly.