Is using an iFrame in a jQuery Lightbox solution bad practice? What is best practice?

At my work, we are having an argument about a lightbox solution. I am in favor of having the html / image / flash displayed in a div, without the need for an iframe, as this adds overhead with re-downloading css / javascript (which is required if it is to maintain same styles and functionality). The benefit of displaying in-line in a div is these scripts and styles don't need to reload. The guy I am arguing with thinks it doesn't matter. In addition to this, there are some slight UI issues with the lightbox solution, which also don't seem to matter to him. Just wanting to know what people believe is best practice. It also seems as if many jQuery lightbox solutions lean towards iFrames, so am I off the mark?