Hi Paul:
After searching high and low for a solution that allowed IPTC and boolean searching as well as lightbox functionality
I found:
4Images
It's quite robust in what it can do.
The big thing for me is it can import the IPTC metadata from a group of uploaded images automatically. No need to caption each image individually.
That really helps if you already have a big archive.
It's PHP based.
I'm still working on it but you can see it in action here:
Sorboimages.com Search
It's also has great support from the author and the users.
My experience with PHP/MySQL is nil so that's really helped.
Oh and it's free though, you can purchase a license for commercial applications.
Rob Sorbo