Same plane. The Warhawk is the US version, the Kittyhawk is the UK/Commonwealth version. I think the Kittyhawk might have been built under license, but they're essentially the same plane.
-F-
"It is obvious that you have greatly over-estimated my regard for your opinion." - Me
If I recall correctly, the Aussies manufactured their own Kittyhawks in limited numbers. However, they also received warhawks from the US. No real difference in the two airplanes.