Microsoft Sudoku

Load up any puzzle and make sure that there are at least 7 7s that need to be filled in. I used expert to have more numbers available to fill in, but you could get this on any difficulty. I turned on all the helpers on the left hand side and went through and filled in all of one number at a time, leaving the 7s for last. Will unlock immediately.

*edit* It's worth mentioning that if you have less than 7 7's you can just keep placing them and removing them and placing them again until you've done it 7 times. from T Svectra T

This one is a little tricky, but doable.

1). Select an Expert puzzle.
2). Once the puzzle opens, look at the numbers below the puzzle. It shows you specifically how many of each number is available to place on the puzzle's board. Make sure that the number seven displays a smaller seven above it, indicating that there are seven sevens available for placement on the board that you are playing.
3). Select 'Menu' to the left of the puzzle. If there are not seven sevens available to play, select 'New Game' until you start a new puzzle that does have. Once a seven-sevens puzzle is started, open the Menu again.
4). Select 'Show All Notes' from the Menu.
5). Select all the "cheats" to ease the gameplay. Block Duplicates, Show Incorrect, and Show Guides.
5). Use the tiny numbers that are now displayed on the board (Show All Notes) and the "cheats" as a guide to help you select every number other than seven within the board. Make sure that you do not type seven!
6). When all numbers have been placed except for seven (or more) sevens, place all of your sevens, finish the game, and watch your Achievement "bing"!

:-)

When you read the achievement description very literally, this becomes very easy!

Start a very easy puzzle, and check that there are at most seven 7s on the board already. Work your way through the puzzle, until you have only one square to fill in.

Then, erase two of the 7s that you entered. Complete the last square. You will now be left with a competed board with the exception of two squares, both of which should be 7.

In one of those squares, enter 7, then erase it, then enter 7, then erase it ... do this at least six times (but probably more to be on the safe side). Once you've done it enough, enter 7 in this box and the other remaining box to complete the puzzle.

DING!

Start up a Expert puzzle since there would be less numbers that are already filled out for you when you start the game. You must have a Expert puzzle with seven sevens to fill in. If not, start a new game over and over until you see 7 with 7 places to fill in. Fill in the numbers but never press the 7 key until there is only 7 blank spaces. Make sure to click the "Show Incorrect" box to fix your mistakes if not clicked prior filling in the numbers. After putting in seven sevens, the puzzle will be finished and the achievement will unlock after you go to the main menu.