CSS / HTML expert

I have a current site that is coded and live but needs to be updated so it's completely cross browser compliant (all major mac and windows browsers). The code needs to be updated and then implemented into the current site store template. The site is using the PHP/MySQL cart Interspire Shopping Cart. You can view the current site at [login to view URL] The following browser compatibility must be attained: Windows - IE 6,7,8 FF 2,3 Safari 2,3 Opera 9 Mac FF 2,3 Safari 2,3 Opera 9