I'd appreciate it if someone over there could tell me how far away it is from the main stuff.

That's not very central -- it's a couple of miles from the city centre. You have to zoom out twice on that map before you can even see things like Kings College Chapel (it's marked).

I have an SE P800, which I assume would work on most networks in Europe. How feasible is it to use a cell phone while travelling to various countries?

It should be fine hardware-wise; you'll need to check with your home provider whether you have "roaming" enabled. (Or even "limited roaming", which just lets you phone home when abroad.)

If you haven't roamed before, or have only recently had the phone, there may be a deposit or other charge to pay to enable roaming. It's still likely to be less than forking out for a native SIM though. (This is the opposite advice from over yonder in the Africa thread, because third-world countries are often much arsier about roaming than European ones are, and much more in favour of you buying a native SIM.)

Peter