In form design view, select the command button, and if the Properties window
is not already visible select Properties from the View menu. You'll find the
Picture property on the Format tab in the Properties window.
I don't know what pictures would be appropriate for your application, but
you can find pretty much anything by searching the web these days. Try some
of these ...
http://www.google.ie/search?hl=en&q=free+icons