I'd make a small image of a wood texture, then make sure that it can tile.
<table background="frame_picture.jpg" cellpadding=10 border=0>
With the code above, the picture frame will be 10 pixels thick. This is the easiest way I can think of. If you want to mess with it, you can also try it this way: create different images for the top, bottom, left, and right sides of the picture frame, and put each in its own table cell as backgrounds. That way you can make it a little more realistic with shading and dimension.