Change the look and feel of existing Zen Cart e-commerce site

Existing website running ZC 1.5.1 Has been developed in an ad hoc fashion without using overide system. Has multiple integrations running in background (CRM etc) Task is to give main landing page and header a new modern look using HTML/CSS whilst leaving underlying structure in place. Needs someone with PHP, HTML, CSS and Graphic skills. Theme will be around existing logo. Main page/header feel shuld be reflected in catgory and product pages.