How to Create a Grid in Photoshop

I wanted to make a grid to lay up 32 cm (1.25") squares with a space of 1 cm between each square. The Photoshop Help was no help, so here's what I figured out to do in Photoshop (this assumes you know the basics about Photoshop as I haven't gone into complete detail):

1. After much trial and error, and being decidedly mathematically challenged, I created a new document 35 mm by 35 mm. (to get about 1 cm of space betweeen the squares)
    
2. I went to: Select » All
    
3. I chose Edit » Stroke. For Stroke, I entered a value of 1 px; in the Color box I chose black, because I wanted to be able to easily see the gridlines. For Location I chose Center, then clicked OK. I then created a second line using the rectangular marquee tool to create a marquee 1 cm inside the edge & again Edit » Stroke (using all the same selections in the dialog box.)
    
4. I chose Edit » Define Pattern and named it 35 cm grid, then clicked OK.
    
5. I created another file that's 8 1/2 x 11 and 300 dpi.
    
6. I created a New Layer.
    
7. I went to Edit » Fill, chose Pattern, then chose my pattern. (Under Blending the Mode is Normal and Opacity is 100%)
    
8. I then manually centered the image on the page.
    
9. Choose File » Print. I got a notice that the image is larger than the paper, but it doesn't matter how it crops since the image is centered on the page.

If you'd like to just use the grid I made, here's a .pdf file of the 8 1/2 x 11 sheet.