Passively converting from PS/2 to USB or USB to PS/2 is only possible with mice and keyboards that are compatible with both PS/2 and USB connections. The following are two ways to determine if these products will work for you:
You can use the USBPS2PC to actively convert PS/2 keyboards and mice to USB.
Note: StarTech.com PS/2 adapters are only officially supported by mice and keyboards.