Very Simple HTML issues

I have PHP based website [login to view URL] When I run this through an HTML checker [login to view URL] It shows an enormous number of errors in the websites compatibility with browsers, speed of loading etc. You can see one of these effects if you load it in FIREFOX (no apparent problems) and the in Internet Explorer (right hand side is at the bottom of the webpage. I need this fixed ASAP. First come (with the right experience and qualifications) first to get the job. Look at the errors first using the website link given above - there seems to be around 80 errors in total. The HTML is created from a PHP script with a MySQL back end. I dont expect that you would have to change the database - just perhaps the PHP that generates the HTML.