Hello,
Incredibly small issue - the CMS creates paragraphs using <p align="left|right|center|justify">, but this is deprecated when trying to be HTML4.01 valid. The workaround is to either use a CSS file, or to write something like <p style="text-align:left;">.
You can find more info here:
http://www.w3.org/TR/html4/present/graphics.html#h-15.1.2
I only started using silverstripe today - am quite impressed with the ease of developing a new website with a modified template.
Cheers,
Jonathan Giles