@jonny,
The tricky part of the boulder question is simple, actually.
The fact of the matter is, God is not human.
To question whether or not He can lift it--or commit suicide for that matter--would be to assign human limitations to something that is not human.
Ultimately, how God operates and lives is completely incomprehensible to us, for we have never experienced anything like it. Therefore, to question it is pointless. It goes back to the table principle.
We are 2 dimensional objects trying to understand God, a 3 dimensional object.
It's impossible.