Internet Explorer CSS fix for website

Hi

I have a website which displays as expected in Firefox, Chrome and Safari but has some strange compatibility isssues with Internet Explorer

For an example please look at the following site www.harrisfootwear.co.uk

and admin area also has issues - www.harrisfootwear.co.uk/admin

For reference The site was developed in OpenCart Version 1.4.9.4. It cannot be upgraded at present because it has been linked to an epos system and has a few customisations

Work i to start immediately. Please confirm you can start straight away and time to complete fix

Thanks