It sounds like css issues. Your lighterbox is probably adding css that is affecting things. If you add a css file for it, add it at the top above the main css and that may help. You can also override stlyes for IE 6 or IE 7 using the IESpecific.css for IE 6 and IE7Specific.css for IE 7 to override the main styles to solve the problem.
Hope it helps,
Joe