If you are getting the same model laptop back with the same specs, it would be best to have them remove the hard drive and give it to you before sending it in for repairs.
I would never send a PC in for repairs with a hard drive in it (not only because then do not need a hard drive to repair it, but also they should have no access to any of my customer's information). At the very least, I would create an image (backup, like with Norton Ghost) of the drive, store the image on an external drive, completely wipe all data from the hard drive with something like Kill disk (normal deletion does not actually delete the files), then send it in and put the data back on the drive with the image when it comes back.
You wouldn't be able to boot from it with different hardware though, even on an external drive (like if you connected it to a different PC), it'll probably just BSOD from having different hardware/drivers.