For a Floyd or floating bridge to play correctly and be properly intonated, you need to adjust your spring tension first, then the trem posts second...
If you're tuning down that low, you may also need a slight neck adjustment, but we'll deal with that later...
1. Make sure your trem is paralell or level to your body. If it is not, remove the plate on the back of your guitar covering the trem route... Tune to your desired pitch, then check to see if your trem is level with the body... If it is not, djust the springs (attached on to a 'claw" that is screwed into the body).
Tuning down will give the springs less tension to counter against, and the back of the trem will be closer to the body than the pivot point at the trem post.
To correct this, turn those screws counter clockwise. This will release some tension. Re-tune your guitar to your desired pitch using a tuner and check to see if the trem is paralell to the body. I would reccomend 1/2 turn at a time per screw. Try to keep the claw relatively paralell to the route.
Retune your guitar, and once you've got that done, check your action. If it's still too low or too high, you will probably need to adjust the trem posts...
Turning counter clockwise will raise the action, and clockwise will lower the side of the trem with the screw.
Adjust to your preferred string height.
Hope this helps... I'm tired... time for bed.