I have a need to build apps for an iPad but I do not have a Mac, is it possible to run the Apple SDK on a PC, through an emulator or some other method?
To build an officially sanctioned and Apple approved application, you need to build that application on Apple hardware.
No easy way around it.
You can install the latest version of virtualbox for windows and run mac os on it. See http://www.sysprobs.com/install-mac-snow-leopard-1063-oracle-virtualbox-32-apple-intel-pc
A little clunky right now, but virtualbox is supposed to add more support for the display resolution and other integration features. Just make sure you make the virtual disk big enough > 20gb.
Just a little more details. Apple SDK is gcc-derived multilib toolchain compiled to run on Darwin like systems + Cocoa & friends (headers and compiled libraries). All these frameworks and binaries are multiarch MACH-O binaries which simply won't run on non-Darwin platforms. So this is not superficial restrictions, simply SDK will not run.