I never said that the "Fix" button returns the settings to the 1" defaults. If you set all the margins to 0" and then allow Word to "fix" them, the results will be the minimums specified by the printer driver. On laser printers, these can be quite small
(although, even so, they don't always reflect the true capabilities of the printer since settings for the same printer can vary depending on the OS/driver); on inkjet printers, the margin for the trailing edge (bottom or one side of landscape pages) will often
be quite large, usually at least half an inch. If the OP is not satisfied with these minimums, then his only recourse is to use Graham's macro.
Here are a few examples from the printers I have installed:
HP LaserJet 400 M401dn PCL 6: 0.17" on all sides
Brother HL 5370-DW: 0.17" top and bottom, 0.25" both sides
HP LaserJet 4100: 0.17" top and bottom, 0.24" both sides (Windows 7)
HP LaserJet 4100: 0.17" all sides (Windows XP)
HP LaserJet 4: 0.17" top and bottom, 0.25" both sides
HP OfficeJet Pro K5400: 0.47" bottom, 0.13" top and both sides
HP DeskJet 820Cse: 0.04" top, 0.46" bottom, 0.25" both sides
HP DeskJet 6122: 0.07" top, 0.5" bottom, 0.25" both sides