Hot-swap capability is a function of the controller and any RAID-management software you choose to use. One thing to know is that hot-swapping is SCSI only since IDE can't handle having a broken connection.
For the drives themselves, you'll want 80-pin SCA drives. These have a single connection on the back for power and SCSI and the device ID is set by the cage it's mounted in. Some companies also might make cages that wil support 68 pin drives by mounting them in a rack, but I don't know of any offhand and I'm not sure how those manage device ID settings.
Lian-Li makes a couple of ATX cases that have removable drive bays out of the box. Check out the
PC-626 and the
PC-72.
/Atx