Edit: Oops, I reread the OP. Yeah, that should indeed work.
Some usb to ps/2 adapters may have limited funcition for use as keyboard hack/keyboard encoder adapters. A problem I encountered while using one of these was that when I tried to hold an input, such as a joystick direction the computer would stop responding after a second or two and my game character would stop moving until I centered and re-threw the joystick to the direction. I looked in notepad and saw that all the other keyboard inputs also stopped repeating their characters after a set amount of repeats; I think it was 16. I am not saying that you will definitely have the same problem, just a warning that not all USB-PS/2 adapters are created equally, and that some are not suitable for games that require "constant" inputs.