Windows 7 drive (P:|)shared with Everyone but not accessible by Windows XP computers on our network

"Try this on the Windows 7 machine:

Open Administrative Tools -> Local Security Policy.
Click on Local Policies -> User Rights Assignment on the left.
Double-click ""Deny access to this computer from network"".
Select Guest and click Remove.
click OK.
EDIT: Ensure in the Permissions for the network share, that Guest is included, since it's no longer part of the Everyone group.
Use regedit to go to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System and create or modify the value of LocalAccountTokenFilterPolicy (32-bit dword) to 1, so the remote logon token will not be filtered (see here)."

Also, there was an update for Windows XP a few months ago, which is needed to be able to connect with new versions of windows. check in windows update center, if you have all updates + service pack 3 installed.

"This is a workable but ugly workaround:

Change the user account type to administrator and set a basic password, ""pass"" for example.
When my XP machine asks for username and password I type [computername]/[admin user name] and the password you set.

This allows you to log into the machine although it may not be great for all occasions (and have security side effects)"