ironware,
search the forum with the name of your template provider and you may find some insight as to whether or not you can make it work. If you're using a Template Monster template the outlook is bleak at best.

I have found that IH2 and lightbox is not workable on my new sites using 1.3.8a and 5.2+ PHP. Probably something in the lightbox code.

I have taken most of them to Fual slimbox or disabled lightbox altogether.