If you buy an LCD TV
1) You can use it to waitch TV without using the computer
2) The PS/2 will plug straight into it
3. It'll alraedy have speakers
4) but you will need a seperate digital TV box (Sky or Freeview)
5) Make sure you get one that is also suitble for use as a PC monitor - some cheaper ones aren't.
If you buy a monitor
1) You will need a TV tuner card
2) You will need a monitor with speakers or you will need to buy speakers.
3) Ypou will need to have the computer running to watch TV
4) I have no idea how you would connect a PS/2 up to it.
Personally the LCDTV option seems easier to me.