It is very annoying to manually change page sides whan you want to print on both sides.
On Windows XP and Vista that have Plug and Play Print Driver Package HP drivers installed, there is an easy to find option (Two-sided Printing) under Print > Preferences > Printing Shortcuts tab.
Unfortunately, on Windows 7 the only driver available is the one coming with Windows 7 but there is no such tab and the closest option to it, is to print duplex manually.
But you don't need to search for additional HP printer drivers, Windows 7 already has support for both side printing, it only needs to be turned on!
So here are the steps to fix this:
1) Click on Start
2) Click on "Devices and Printers"
3) Right click on the printer listed there
4) Click on "Printer Properties" (not "Properties")
5) Select "Device Settings" tab
6) On the "Installable Options" there is an option named "Duplex Unit (for 2-sided Printing)", select "Installed" from the drop down menu
7) Press OK
That's it! Now you can print automatically on both side without anoying manually page changing by selecting: Print > Preferences > Finishing tab > Print on Both Sides