This is as straightforward as setting up a network printer from Windows XP.
First of all you’ve got to set up a private network connection between the host and the guest operating system.
Then you have to make sure that CUPS is accepting connection from other hosts.
When finished with all this foreplay, you can go ahead and use the printer from Windows XP. Boot your VirtualBox and enter Windows XP. Go to Start -> Settings -> Printers and Faxes. Click on Add a printer. Tell the wizard that you wish to add a network printer. Specify that you want to Connect to a printer on the Internet or on a home or office network. Specify the URL of your printer. It should be something like:
Where in printer-name you should replace the name of your printer. Complete the installation of your printer by specifying the driver to be used. You should now be able to print from your Windows XP now.