Today 12th September 2008 I finished working on a media centre website at my office. I had a good time with it :) as I got permission to use my favorite CMS SilverStripe for that.
The website is http://staysure.co.uk/mediacentre/ have a look, You will feel that SilverStripe can cater most of your website needs after looking at it.
The most important thing it that I found some good hacks for the TinyMCE editor that they have used there.
2) I needed to take off validating html on the TinyMCE but the SilverStripe editor doesn't allow me to do it.
In that file you can find some useful things.
1) the html tags which are allowed in the editor that can be controlled by the directive valid_elements which you can find at the line 43.
2) Validating HTML can be disabled with the verify_html directive at line 42 there.
I thought that these tips will be useful for you.
Give a try ;).