Hi
Joomla 1.5.x used old structure, so in practical way it's very hard to get good quality code.
I suggest ask your client for migration to J3.3.6+ - you can even use this same, or very similar template.
New Joomla have better quality code which cases also better support for WCAG.
and it's easier to implement more improvements.
Joomla 1.5 is very danger if you don't have strong server security and tool like Rsfirewall or similar installed.