Hi mitchelle 65,
Make sure that you have an identical UserName and Password on XP and 7 computers.
Compare the ipconfig /all make sure that they are on the same Subnet, and keep on eye on the 'Peer to Peer' Node Type, then you won't be able to network the 2 or do files/printer sharing. It's fixable using a registry edit.
If you have any Security/Firewall Software running on both computers - Norton, McAfee, Zone Alarm or similar, pls. disable it for now.
If you are using the built-in Firewall, make sure to exclude Files and Printer sharing from the Windows Firewall exclusion Tab.
Do some test also, make sure that you're able to ping each others IP Address (info. can be found from ipconfig /all)
When you share a drive or folder, give a Full permission for now and see if you can access each other's shared drive or folder.
Try accessing each other's file or folder by typing these:
Click on Start=> on search box type \\computername\shareddrivename
or sharedfoldername press enter. The computername can also be replace by an IP Address of the computer that you're trying to access.
Hope this helps.