For capturing I can only offer the advice of great patience or a cheat plug-in if you lack patience.
Disabling is another manner. First, find yourself about two hours. Then follow these steps.
- Hold your escorts far away, they'll just get killed for nothing.
- Stay far away, destroying all fighters except one.
- Disable that one
- With escorts, swarm the Dreadnaught and take down its shields
- Repeat step 1
- Use rockets to disable the Dreadnaught from outside of its range.
- If you run out of rockets, board the fighter, then lure the Dreadnaught back. It will rearm the fighter and send it back after you. Repeat steps 3 and 7.
Good luck.