You'll get many different answers I'm afraid.

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1) Why are they really increasing?

Oil is a traded commodity, thus there is quite a lot of speculation going on.  Any news or uncertainty linked to supply tend to drive prices up.  

2) Is Bush in part responsible for the price rise?

To the extent that the current Middle-East policy is driving uncertainty yes.

3) Is the amount of oil on earth running out to where it makes the prices go up?

That's not why they are so high right now.

4) Why does it seem there is no real huge push for switching to another energy source for motor vehicles?

I'd say there is a real push for it, but Oil is remarkably effective and inexpensive. It's not an easy energy source to replace.  Thats not all, even if all cars ran on lemon juice, Oil is still very much a part of our lives in that it's used to make plastics.

Here is why:

http://www.cathinfo.com/bb/index.php?a=topic&t=2089


http://www.cathinfo.com/bb/index.php?a=topic&t=2088