You can buy off the shelf cameras which are designed to output a signal compatable with television. I recently bought a TINY little camera for £30 which does just that - it's colour and it even has audio pickup on it. All you need is a set of RCA leads to interface it to the composite and Audio in ports on your television.
If you're asking if there's a way to get a webcam to work on your TV, then the answer is no. Certainly not easily, and why would you want to when you can pickup cameras specifically for the purpose even cheaper.
Brian