Is Xcode 4.2 available for a MacBook Pro 2.2 with a Core Duo processor?
Yes.
This rather depends on the OS version than the Mac. Since this Macbook has a 32-bit processor, the latest OS you can install is Snow Leopard. The latest version of Xcode is still made available for Snow Leopard by Apple.
Xcode 4.2 for Lion (Mac App Store)
Xcode 4.2 for Snow Leopard (direct link)
Xcode 3.1.4 for Leopard (latest version that runs on Leopard)