I have a piaggio typhoon and i wont to fit 13" wheels from a nrg do i need the forks to fit the wheels?

Answer 1

Yes, you will.

The NRG forks won't fit on the Typhoon, though...

Answer 2

You could get the hubs machined to match your exsisting forks. You'll also have to check clearance between the new wheel and the mudguard/frame of the bike. If the new wheels are wider than your current ones, it will cause all sorts of engineering problems! Also if you have a disk brake fitted you will have to re-mount the caliper to allign with the new disk.
Changing the rear wheel will change your Typhoon's acceleration, top speed and fuel consumption.
Why do you want to change the wheels? Modern bikes are now designed to perform the best they can, if you start messing about with wheels and forks and changing the geometery without knowing exactly what you're doing, you could end up with a slower, poorer handling bike! If you really want to do it, it would be best to try and find someone who has already done it, and talk to them. These things are never as simple as you first think!