Doug,
Did you use the hyperlink button, when configuring your "Custom Attribute Display" pop up box?
[ATTACH=CONFIG]25902[/ATTACH]
If you have a filed in your attribute table dedicated to those file locations, you can put the field name in the URL location with {} surrounding it. i.e. {TEXT}
But remember if it is stored on your machine, it will only work for you.
Hope this helps!
Tim