Valid XHTML/CSS translation for www.carlist.ie

We have an existing HTML/CSS design for [login to view URL] which renders correctly in Firefox 2 but does not render correctly in IE 6 and Safari. We would like a valid XHTML/CSS version of the site (2 pages) which will render correctly in Firefox, IE 6 & 7 and Safari. It is also desirable to reduce the number of images loaded on first page load - can the rounded corner graphics be placed in one single image? Some small changes to the current design are also required: - The green filter should have rounded corners - The grey box at the top of this page should have rounded corners I will also be looking for a number of similar designs in a future project.