Easy C driver problem

I have installed/reinstalled the USB-Serial driver numerous amounts of times in the hope that it will work on my Vista PC, it worked the first day I used Easy C, but since then has not been able to work. I install the driver properly, and try to locate the COM port, and it says a driver needs to be installed, even though it already is. What do I do?

Here is the driver we sent Kyle that seemed to have helped with Vista.
vista-prolific.zip (1.77 MB)