Hi there
Try this.... I used PhotoShop for mine... you commented on it earlier today.
All you have to do is open a new document and size it about 8x10 (or whatever you choose).
Then open 9 photos that you want to use. Re-size your photos to about 3x3 square or smaller. There may be a better way but I'm still learning myself.
Next go back to you main document and choose view/show/gridlines.
Now just click on your first photo and drag it to the new document. Count the grids to decide how large or small you need to size the first photos so all the photos will fit evenly. The click (Control-T) and resize the photo accordingly . Press enter when you get it the way you want it. Start in the upper left corner. I usually leave at least 4 grid lines above my top photo and 4 to the each side.
Drag the following photos into your grid and as you drop each one in, press (Shift-Control-T) and the computer will re-size it to the same proportions as the first photo (as long as they are all the same size to start with).
Now that they are all in the grid and sized to perfection, you can move them around as you choose. If you need to resize something, you can go to (Edit, Free Transform) and then click and drag to your hearts content. Just be sure to hit enter to save your selection.
When you all done, remove the Gridlines, and add some Text to the bottom and WAAA-LA... all done!
Good Luck!!