KVM and USB

I have been using a KVM switch between my desktop and laptop for about a year. All keyboard and mouse connections are PS2. Got a new laptop that has no PS2 only USB sockets. Got a PS2 to USB yadapter, but the keyboard goes haywire and un useable, eg, keys don't responded; bringing up start menu it sort of does a scrolling flash. I suspect that the problem has to do with the fact that the USB is putting out some power and confusing the switch. What are my alternatives to being able to use the same monitor/keyborard/mouse with a PS2 style desktop and a USB only laptop?