UDK is 64-bit compatible******warning caveat below!

((The UDK is designed for 64-bit workstations. Lightmass creator is 64-bit. However, what the UDK outputs is all 32-bit. So no, not everything is 64-bit... but parts are, and everything is designed to run on 64-bit PCs.))

So if you have a 64-bit machine, you can run UDK no problem what-so-ever.