If you are using Port 631 for IPP printing, you may find that your firewall may not let the print data through. If this is the case, use a different port number (port 80), or configure your Firewall to allow Port 631 data through.
     

To send a print job using IPP to a printer using Port 80 (the standard HTTP port) enter the following when configuring your Windows 2000/XP, Windows Vista and Windows Server  2003 system.

http://ip_address/ipp