[UPDATE: David Sánchez has a much easier method: run system-config-printer as root (it's installed in Wheezy). From there select the network printer option.]
Debian Wheezy has a reasonably up-to-date version of HPLIP (3.11.12. Latest is 3.12.2) so it should support my year-old printer. It recognises the printer but says I need to be a member of so-and-so group.
Where is users and groups in Gnome 3? Maybe I need gnome-system-tools? OK, now I have Users and Groups in System Settings, but I can't see groups. But in User Privileges I can see Configure printers. Ticking that and I can add the printer. Make the printer the default printer and I can print too.