You're going to want heavier gauge strings to keep the tension level playable... i.e. so you won't have floppy strings.
Larger strings=more tension. Floating bridges will need to be adjusted. Remove the trem cover on the back of the guitar. Adjust the spring tension first. Do this by adjusting the two screws holdingthe spring claw into the body. They will need to be tightened. Apply 1/4 to 1 turn on each screw, then retune your guitar. Keep doing this until you're tuned where you want to be and where the base of the trem is omewhere between parallel to the strings.
After the guitar has settled (a day or two), you can adjust your neck to get the best string height (if desired).
The intonation is the last thing that really needs adjusting and is the most important. Any good strobe tuner should work... I would avoid using a handheld tuner to intonate, they're just not precise enough.
If you don't know how to do any of this, have it professionally set up. If you're intonation is off, you're going to sound like shit playing with another guitarist.
Darthlardo, As for having a guitar that you can go from standard E to standard Eb, that all depends on the guitar. Some can take those adjustments just fine,others seem to have a bit more problems. IF it's a guitar with a floating trem (floyd, edge, etc..) then it should be blocked, or it'll be a pain going back and fourth.