How to enable iOS 4.3+ multitasking gestures on iPad?
Both the latest Xcode 3 and the latest Xcode 4 allow you to mark an iPad with the latest 4.3.x as being "used for development". You can cancel if asked for your developer program credentials (which cost $99) and still have access to the gesture switch on the iPad.

Xcode 4 is only available presently as a $5 download from the Mac App store or with the $99 paid Mac Developer program as a restricted download. The free developer account (which still allows you to get Xcode 3) is fairly painless to set up as long as you can agree to all the conditions. You can see the various free and paid programs at http://developer.apple.com/programs/which-program/ - it used to be simpler but the free account is still fairly powerful but not on the cutting edge with pre-release

As with anything that is in software development, all things subject to change often and YMMV.