The thing with the USB keys is that EVMOVE won't allow you to put the keys onto a "removeable drive." Most USB keys are recognized as removeable drives by Windows 2000 or XP. Back in the day, you could get around this with a dumb USB key and a dumb operating system like Windows '95 or Windows '98. Now, I don't think there's a way to do this with XP.
But wait! Call your local rep. Since RA has been threatening for years to get rid of the current activation scheme for RSLogix, I am pretty sure that they can sell you a USB key that is formatted to hold the license and let you activate different computers by plugging it in. In fact, I think I have one in my drawer that I got over a year ago and have never used. Yep. It's a "USB Dongle Kit V1.00.00." Guess that's why I've never opened it... never use V1.00.00! The PN is 9509USBDONG; call your rep and ask what the deal is with these, I think it's intended to solve your problem.