Our experiments need to be designed with two response pads (left and right). Both those pads have a RS-232 connector which then feeds into our present response computer (IFIS). Our lab is thinking of switching to Inquisit to do our experiments.

I thought that one way to use both those inputs would be to use a dual RS-232 to USB converter and configuring the USB port as a COM port. Has anyone dealt with this hardware design before?

Given the technological differences between RS232 and USB (see e.g. http://www.lammertbies.nl/comm/info/RS-232-usb.html) I doubt this will work. If I were you I'd rather consult with your institution's tech shop and have them mod the two response pads to use a single parallel port interface (much like http://brm.psychonomic-journals.org/content/39/4/797.short).

~Dave