I have found a device that will allow me to have 2 external screens, my only queries are... will it work with an ATI Radeon HD 2400 graphics card and does the fact that I got my iMac in England mean it will still work with this product you can only buy in America?
http://www.atpm.com/15.08/owc-usb-display-adapter.shtml
http://www.atpm.com/15.08/owc-usb-display-adapter.shtml