The other method that I use that doesn't involve having to get or learn a new piece of software is to use Microsoft Excel. What I mention below is based upon using US 8 1/2 x 11" paper and not A4... but assume you can adjust the margins differently so that the results are the same
You first start by opening a New Excel spreadsheet and then go in to change the margins. Since we want 1" squares... you set the left and right margins at 0.25". This gives us 8" of usable left-right space. (8 1/2" wide paper - .5" from both margins = 8"). Then, set the top and bottom margins at .5" (giving us 11" long paper - 1" of margins = 10"). Your printable area on each sheet is now 8"x10" (or 8 squares by 10 squares).
Next, you highlight the entire sheet and expand the columns just enough such that you get 8 columns per page. For my Microsoft Excel 2003... that ends up at 9.89 column width (96 pixels). You then expand the rows to get exactly 10 rows per sheet (for me it's 72 row height or 96 pixels). This will give you sheets that are 8 columns by 10 rows out to the edges of the margins, or rows/columns that are each 1" square (or nearest you're going to get). Save this sheet as your template.
From then on... all you need to do is open a map image into the template sheet, then expand the map as big as you need so that the map's gridlines are as close to matching the spreadsheet's gridlines as possible through as much of the map as possible.
You thus have expanded your map to get its grid to 1" squares, and when you then print it, you'll get the map split up onto individual 8 1/2" x 11" sheets that you can then trim the margins off of and scotchtape together.
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It's a little bit of work, but its the easiest way I've found to expand maps to 1" grids without spending any money on any other printing or 'shopping programs.