I did it
In 1999 I decided I would switch to fixed wing since I got a great opportunity to go fly for a fractional ownership program in Beechjets as SIC, so April 10 1999 I arrived at the FlighSafety/Raytheon training facility in Wichta, Kansas, when I arrived I had about 250 hrs TT in airplanes, all in nothing bigger than a Piper Seminole, I had also not flown an airplane in about 5 years at all.
Guess what? 10 days later I had my FSI diploma, and about a month later I had about 60 jet hours and felt as comfortable as if I had been doing all my life! The hardest part was learning to program those stupid FMS's, and keeping the plane clean! If you have considerable helicopter time, "flying" the jet will be really easy, you will have excellent "feel", be really smooth at the controls, make excellent landings.
The hardest things for me were:
1. Learning that you have to plan early, Beechjets do 100 NM in about 15 minutes, so things happen faster than you are accustomed to.
2. Controlling airspeed, those light jets could glide forever at 350 Kts, losing extra speed when you are in a descent is practically impossible sometimes.
3. Convincing other pilots it is possible to fly the airplane w/out autopilot, its boring though.
4. Getting used to boredom, I was used to start working after the takeoff in helis, in the plane its the other way around, Me and another pilot actually fell asleep flying from Seattle to Tucson one day at around 3 oclock in the morning, the overspeed horn woke us up!
PS: A year later I decide it was not for me and came back to helicopters, went to Africa to work for EHI