SwimJim:DA Aquamaster gave a very good description on how its done. We also have a safety diver hooked up and ready to go as well. Ice diving, although is alot of work is also a good reason to get together and dive with you friends in the middle of winter when there simply isn't anything else going on. Its as much of a party as it is a dive usually. A proper ice dive means hot chili and other good things afterwards. Sure beats the alternatives, which is nothing. Ha
SwimJim is correct, when we do it, we do it as a club event and the one or two dives we do are just the excuse to show up mid winter with other crazies and have fun, eat chili, etc. And practically speaking, you need a minimum of 4 people do to it anyway, so you just as well make it a full blown social event.
There also seems to be some variation in ice diving procedure. I was originally taught to secure the line to the ice with an ice screw and then use a safety diver sitting on the edge of the hole attached to a slightly longer line. However many of the PADI rec divers and public safety divers in the local area rely only on the tender to hold the line and also use two divers in the water at the same time. In my experience, two divers on two lines requires a lot more care to keep them from tangling and makes securing the line to the ice problematic. It also requires the tenders to coordinate efforts and/or move around the hole, which creates the potential for falls, dropped lines etc. You gain redundancy perhaps, but then you also create the potential to need that redundancy.
Personally, unless one of the divers is an instructor and the other is a student, I prefer only having one diver in the water and use the single diver/safety diver approach.