What woody said is true, however, just for general knowledge, you can install one of a few programs that tell you what the kernel version is.

Off the top of my head, Health Check and Conky both tell you what kernel you're running.

I would tell you what to use to get the Kernel version through command-line, but i don't know. It's probably "cat /proc/sys/kernel/(something)"... I tried "cat /proc/sys/kernel/version" - doesn't give anything that looks like a kernel version to me, but *shrug*. Poke around in /proc/sys/, using the cat command on everything in there. cat doesn't change anything, so you won't screw up your system if you don't type anything stupid, but you should eventually find it.