If the whole flange is shot, do you know how it's connected to the PVC? If it's just with a gasket, you could maybe wrestle it out with enough elbow grease. Otherwise you may have to chisel it or saw it out in sections (with something in the drain to prevent all that debris from going down).
Then there's this: http://www.doityourself.com/invt/6714364 I believe you just stick it in over your existing flange, screw it to the floor, and voila.. It says no tear out, but not sure if I'm reading into that correctly. Anyone else familiar with it?
BTW - If your house is plumbed with PVC waste, the flange has gotta be cast iron, not lead, though I'm surprised it's not PVC too.