It's quite simple -- just add the printer to the XP virtual machine as if it were a "Real" machine. Create a new "Local" port and simply add the printer. XP will install its own driver
I've got a number of posts on this forum (do a search) about sharing printers bewteen Windows 7 and XP and between x-86 and x-64 systems.
Set your networking option in the virtual pc to Bridged or NAT so you can share the printer on Windows 7.
With the "Integration" feature it might be even easier -- unfortunately using the Integration feature loses any decent screen resolution on your Guest OS so for me currently XP mode whilst a great idea has "shot itself in the foot" since with decent quality monitors these days the resolution on Virtual PC looks absolutely appaling ( VGA standard on a 28 inch screen looks quite frightening).