Seeking Advice - Flash Site with CMS

Hello,
Am wondering what the best solution will be for a Flash site that also requires a CMS for the client to alter the content - particularly images and text. My first thought was to use XML and teach the client to modify it but they want a UI to do this in. I am more comfortable with XML than PHP but prepared to use the latter if it offers a better solution.

So far as I can see there are two (possibly 3) parts to this:

  1. Flash site running from XML / PHP
  2. CMS Application to used upload images (into a category), add text, etc.
  3. Database?

If using XML, I imagine the CMS app would be built in Flex and output an XML document to be uploaded by the client as well as write/upload the image files as required. I realise this would probably require PHP.

If using PHP and a database I dont really know where to start so advice is more than welcome. Is there a PHP class that does something like this out there?

Hope the above is clear.

Thanks,
Elliot