I use inkscape usually, but I’ve also used visio, which would work fine for making a grid. Visio is not free, however.
To make a grid in inkscape, I would do one of the following:
1. Make a line. Copy it nine times.
2. Rotate the last line 90 degrees and copy it eight times.
3. Use the align and distribute dialog to arrange the lines into a regular grid.
4. Group the lines and resize as desired.
Someone else might know of something else that would work better, but this is how I would do it.
I wanted to double-check my inkscape instructions, and ended up making the attached file. Hope it works for you.