What causes judder in a fiat stilo?

Lifting your foot on and off the go pedal?
Tapping the brakes?
Driving with the windows open?

Seriously though, you'll have to be more specific.
Whilst driving? A hum whilst stationary? Do the revs change?

Its when I lift off only in 1st and 2nd.

Check the engine steady bar - bolts to bottom of gearbox.