Here is some info on a spring over:
Increasing Land Rover ground clearance
Kevin's right though, unless you are wanting to do a powerplant change you wont be running much more than a 33in.
If you want to go the big tire route, plan on lots of mods and a new engine.
Stock gearing is good enough for 32's and if you put some HP mods on your engine, 33's. anything more will make your little 2.25 wheez to death.
But if you want to try, go for it and let us know how it goes.
