I thought you might like a copy of the notes I have written to share files between Win 7 and XP computers. I also use it to get full two way control between Win 7 computers.
Network Windows 7 and XP Computers
There should be no need to make changes to the network settings on the XP computer.
Run Windows Explorer on the Windows 7 computer.
Under Computer right click on drive C and select Share with, Advanced sharing.
Select Advance Sharing and check Share this folder.
Under permissions for Everyone check Full Control then click Apply.
Click OK then OK again.
Under Password Protection click on Network and Sharing Center.
Select Home or Work and turn off Password protected sharing.
Click on Save changes and then click Close.
Exit Windows Explorer.
Double click on the Network icon.
Select Network, right click on drive C of the Windows 7 computer and select Properties.
Open the Security tab and click Edit.
Click on Add and type Everyone and then click OK.
A user icon should appear in the box with Everyone beside it.
Allow Full permission for Everyone. (This excludes Special permissions.)
Click OK.
The computer should then go through the process of setting permissions for the drive folders. The process stops half a dozen times with errors but just click Continue.
Click OK to finish.
Good luck.