Ok, so tried to install the driver for a networked HP 2420 installed on a Windows Server 2003 (PLC6) onto a Windows 7 64bit. The system said something to the effect that no driver could be found and "windows cannot find suitable driver". So what you do is this.
Download the "HP Universal Print Driver for Windows PCL6" and install it on the system. Install it as a universal device, not as specific printer. Then in the printers folder, double click the printer icon. In there you should be able to specify which printer to use and even install it as an icon in the Printers/Faxes folder for use in other applications.
Email me if you have issues with this printer specifically.