I have a 1991 4 x 4 Ford Explorer that I need to replace the front brake rotors on. Extreme runout and they have been turned before I got the vehicle. I know how to remove wheels, pads and calipers. My question in this. Are the rotors pressed onto the hubs or is there a method to get the rotors off with the hubs still on the car?

This link does a pretty good job of explaining what's typically involved:

Yahoo! Video Detail for 92 Ford Ranger 4X4 Front Brakes / Rotors/ / Bea...

It's a fun, easy job. Remove the master cylinder reservoir cap, prior to trying to spread the brake pads. Clean the old bearings with kerosene or Stoddard Solvent. Afterwards, it's fine to blow the old bearings off with compressed air--just don't spin the bearing. I would repack the wheel bearings with full synthetic wheel bearing grease (e.g. Mobil 1, Valvoline SynPower, or Amsoil GLC). This will provide better protection and gas mileage (less friction), which is important on 4x4s. The job goes easier if you use a pair of Lisle LIS44900, MAC P22A, or Craftsman P4735 Lock Ring Pliers to remove the C-clip. Get the torque specs for your truck.

From the video, Looks like the hub is part of the rotor. I wasn't sure. Usually pretty hard to get the bearing races out without ruining them, so it looks like new bearings and races as well. Oh yes, Seals too! Correct? Thank you

Depending upon their condition, you should be able to clean, repack, and install the old bearings and seals. Replace both front rotors, not just one. Install new pads and bleed the complete brake system. Valvoline brake fluid meets Ford's HBH requirements for trucks.