Is Xcode 4.2 available for a MacBook Pro 2.2 with a Core Duo processor? I'm trying to figure out if this computer will be able to run the new Xcode 4.2.

These are the specs:


MacBook Pro 2.2 15'' Core Duo 2.16GHz (T2600)
2 GB RAM


The full specs can be found here.
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)