I showed a developer a site that I liked and wanted something similar. Well it looks like the developer copied their source code and made changes to the images. I would think there are some copyright issues here. How original does a "clone" site need to be to avoid legal issues?
There is really no rule of thumb that can be provided because the law, at least in the US, says that you cannot defend against copyright infringement by showing how much you did not take. Popular on the Internet are claims that if you are different by 10% or 20% or some X% you are fine. These are unreliable and wrong. The more different you are the better, but the question is whether someone would perceive the second work to be a copy of the original. It is quite subjective. Having said all this, it sounds like you have some problems. Source code can be copyrighted. I hope this helps. For some more information you might be interested in my website: http://www.ipwatchdog.com/copyright/ -Gene
IP rights can be tricky... I would change as much as you can with the design/imagery, since even if you change enough to bypass laws, people still might call you out for it (such as putting the original site + your site up for display on blogs, etc)