If you really want to install only the kernel and nothing else you could get a hold of tomsrtbt, http://www.toms.net/rb/
, which is a small distribution which installs on a diskette. You could then copy its kernel to your hard disk with the dd command, see the man page. The kernel would have to be copied to the mbr which is the first sector on your disk. Like a previous post pointed out, the kernel first looks for a file called init. If this file is not found what you get is kernel panic, in other words it just hangs and does nothing. Google for 'rescue disk' for more information.