Picture Attachment Page. Picture text alignment

The Picture Attachment Page works well for standard screens, tablets, etc, but on higher resolution screens the picture is centered (sized as per actual pixels), while the description text is aligned to the full left and right limits of the screen size. This is visually very poor and also makes it difficult to read the text. (Especially so if the screen is also physically large or displaying on a HDTV).

Here is a link to a sample screen.
http://mattobrienblogcom.fatcow.com/matt_blog/?attachment_id=573

And here is a screen dump which illustrates the problem.

http://mattobrienblogcom.fatcow.com/matt_blog/?p=583

My question.

How can I set the left and right margin of the text to align with the picture.

Or if this is a simplier problem to solve :
How can I set the max description text width.

Looking forward to enlightenment.