Anyone know how? It looks as though there is a large nut holding them on in the center.

 

Are you talking about the dust cap? Thats not even part of the rotor. The rotor has a big hole in the center, it's a real b*tch to get off there but get the biggest hammer you got, seriously. It won't look like it's coming off but it is. I sat there for about 30 minutes hammering the hell out of it with a sledge. It gets rusted on there, but I found loosening the adjustment sprocket in the back hole thats covered with a rubber grommet (it's the parking brake adjustment) probably helps. Regardless, you don't have to do that and it could have been my imagination. Just take the brake caliper off, and of course the tire, and you're good to go. It actually just slides right off...if it's not rusted. Basically, bang the hell out of it.

 

I got lucky. my rears just all but fell off when I took them apart

 

Pull the caliper off and beat the **** out of 'em with a hammer on the center of the flange around the lug nuts. Don't be shy. If you live in a rust free state (like me), they should slide right off with little if any hammering. If not, you'll have to do some serious hammering to get them off the axle.

 

If the rotors are that bad, back off the e brake adjuster if possible (siezed) or like these others said, beat the **** out of it turning it slightly each hit or two.