Is this IDE or SCSI? Very very few IDE support hotswapping, but it's quite usual in SCSI world.
I wouldn't recommend trying this with an IDE drive, especially if you don't trust your drive slide.
If you wish to try anyways, you are crazy, you will kill your drive.
If you _still_ wish to try, well... make sure your slide _really_ cut the power to the drive when you turn off the key (some does not), as hotswapping a powered drive will most likely result in a disaster. Also, never never never does it on a mounted drive (of course). I did it sometime, it's quite possible, but you have to accept that you may kill your drive at any time