If the new keyboard supports ps2 connection then yes! If it doesn't support ps2 connection then nope.
With my previous post I was assuming your usb keyboard came with a ps2 adapter. If it didn't and you bought one, it may not work. Some usb keyboards support ps2, some don't. It's a bit of a lottery as it's difficult to tell if they have ps2 compatability unless it's clearly stated on the box or if they have a ps2 adapter in the box with them!
Have you thought about a usb pci card? If you are short of usb ports and have a spare pci slot then it can be useful.