The easiest way would be to buy a window kit from somewhere like performance-pcs.com and cut the hole with a jigsaw (make sure to use a smooth-cut blade for metal). You'll want to clamp the panel down pretty good and use a cutting guide (a "rip-fence" for a circular saw should work). And cover the area outside of the cut with tape or something so the panel doesn't get scratched by the feet.
If you have a nice dremel or other nice rotary tool, you can use a heavy duty cut-off blade instead of the jigsaw, but you might have a harder time getting straight cuts. However, you can always grind out the areas where it's uneven and then file it down. This is how I did it because I was unable to sufficiently clamp the panel for the jigsaw (it kept flopping up and down pretty bad).
Also, if you don't want to have a rubber grommet like the window kits use, you can buy just the acrylic and cut it to be larger than the hole, then rivet it to the panel. When cutting the acrylic, do not use power tools as it will melt very easy. Instead, score it with a utility knife and snap it. You may want to practice on scrap first.