There may be some help at Microsoft's Find and Install Printer Drivers.

If you scroll down, there's a video clip for "manual installation." Since I don't have a Win7 to look at I didn't probe into how helpful it is.

A Microsoft.com search for HP Printer Drivers "compatible with Win7" finds only THREE HP PRINTERS that Microsoft says are fully compatible. Others - like yours - may be able to use a "generic driver" to do some basic functions, but my experience with that workaround has been somewhat less than satisfactory.

Any chance of swapping an XP that has the driver to the offline use and putting the Win7 on the net as the replacement? "Improved browsing security" is one of the big brags for Win7.

John