We have quite a few hp printers and I noticed now they all use the HP Universal printer driver which I added to the printer server (2003 serveR) but when someone on win7 64 bit tries to install the printer they still get an error that says no driver was found on the server for this printer.
I don't have any problems with our canon's and Dells but they supply a driver for each model unlike hp who is going to this universal driver route which frankly I don't like.
If you go to your Printer Properties and look on the 'Sharing' tab, you will find a button called "Additional Drivers". Click that. In that dialog you can add drivers for x86_64 and Itanium clients. HP publishes a Universal Driver for 64-bit as well.
In my experience, most HP printers do have model-specific drivers if you look for them.
You need to make sure that the driver versions for the x64 version are identical to those of the currently installed driver. You can't use the 5.5 x64 UPD with the 5.1 x86 UPD. They have to be identical. You also can't mix and match printer-specific drivers with a UPD for the same printer. Again, the drivers must match exactly other than platform architecture.
This isn't a limitation of the HP UPD, you'll run into this for any mixed-arch driver deployment on Windows.
Add HP Universal Printer driver of Win 7 on Win 2003? Problem adding Windows 7 64-bit print drivers to a 32-bit Windows 2003 print server
And for HP printer you can also use separate driver for each printer model.