I don't know about how XP is virtually installed in Windows7 but seems it is a separate machine in the eyes of Windows7.
You will need to install the Shared Printer in Windows XP and direct the output to the Printer. Though the machine is running in a Windows 7 Wrapper, windows 7 should not be involved anywhere in the Picture.
There could be two approaches to the situation-
-----You install the Printer on Windows 7 which is shared via Windows Networking. You generate the Print job in Windows XP which is redirected to the Windows7 machine that allows carrying out the Print Job.
-----The Printer is installed locally on the Windows XP machine which directs it to do the Printing. Though Windows7 is there, XP is a totally separate machine on the network unrelated to Windows7 in any way.
Please give a clear layout of the net use commands you are using.
Ravi.