Vista - Can't print with Vista standard user to printer on XP PC!!!

Linksys/Cisco wireless router network connecting:

1 Vista SP1 Home Premium PC (x64).
1 Vista SP1 Home Basic laptop (X86) via wireless connection.

2 XP SP3 PCs, one with Panasonic KX-MB271 printer connected via USB.

I can print without error from the XP PCs and from the Vista PCs as an administrator user.

However, trying to perform a test print (or print from an application) from either of the Vista PCs as a standard user causes the error "Test Page Failed to Print".

All users are assigned to the same workgroup, same networked printer name, and local ports attached to the XP-networked printer.

The latest drivers for XP and Vista are installed.

Printer and file sharing is enabled for all systems.

User permissions for the offending Vista standard users are set to print and manage printers and documents.

I disabled both Windows and McAfee firewalls, but the problem remains.

I tried printing with the Vista laptop connected directly to the network with an Ethernet cable and disabling the wireless connection: same problem.

I reinstalled the latest Panasonic drivers for the XP and Vista systems: still fails.

Now, here's the surreal part: I attached the printer directly to the Vista (X86) SP1 laptop; loaded drivers anew; configured the printer to a USB port; and then attempted to print as a standard user. IT STILL FAILS!!!

However, printing via administrator directly through the USB connection to the printer still works as before!!!

I had a good friend with 15+ yrs. of experience in IT take a look at the problem, AND HE CANNOT FIGURE IT OUT!!!

This problem is driving me NUTS!!!

What is it about Vista standard user and printing?!?!?!?!

HELP!!!!

Thanks in advance.