How do I print with the grid lines showing?

The grid in Elements isn't printable. It's just a visual reference. If you want grids, you will need to do them manually by making a pattern, with a grid paper generator, or a plug-in (filter).

Pattern option tutorials:

http://www.bluesfear.com/tutorials/Grid.htm

http://www.cbtcafe.com/photoshop/newgrid/newgrid.html

Graph and Grid paper generator:

http://incompetech.com/graphpaper/square.html

Note: Open PDF in Elements. Click okay to rasterize paper. Grid is over transparency.

plug in options:

Grid Generator (Windows Only) found here:  http://www.richardrosenman.com/software/downloads/

Grids (Windows and Mac versions):  http://www.users.cloud9.net/~gparet/photoshop/#grid

If I recall correctly, the Grids filter from cloud9 will appear under select instead of under filter in your menu.

You can also turn on the print crop marks option present  in Moe Options dialog box.

• Hold down the SHIFT key while using the brush tool (or eraser, etc.) and you will get a straight line.

• If you access the Custom shape tool, then the shapes library, you will find a rudimentary grid.

If you haven't tried this already, simply find an image of a grid you like.  Drag it into or open it up in Photoshop/Elements.  PS will let you then let you EDIT/DEFINE Pattern, meaning you now have it as a usable pattern. (I assume Elements will do the same). Then create a LAYER and FILL it with the GRID Pattern you just defined.  And voila you have a grid that you can move where needed and can print.  I admit you might have to alter opacity to see it depending on what's in front AND that this is a simple feature PS/Elements should have.

Hope that helped.

Follow-up to tensace's suggestion of defining a grid pattern:

I found a grid at Google Images (there are lots of grids there) and used it to define a pattern.

Add a blank layer and fill with the pattern. Change the layer's Blend Mode to Multiply. The white background will disappear leaving just the grid lines.

Another example of this at http://forums.adobe.com/thread/875370

I am a painter also, and I have found an easy way. I use the crop tool to make the gridlines on the photo, then hit the print screen button on the keyboard. I then load that photo with the lines on it into Photoshop CS6 and print it.

Brilliant! Lame that this big engine can't just let you print them with a click of the mouse though.