ES250 Help Needed

Ok, so Im driving on the freeway and my car starts knocking and then my car cuts off. I roll off the freeway and engine refuses to start. When I turn the key it jus "clicks" and the lights dim. Popped the hood and I find oil in one of the cylinders. Anyone know what this could be. BTW: The car never overheated before it went out.

ouch! A loud Knocking could be pretty serious.. from experiance, I'd say you slipped a baring or one of the head gaskets decided to rip loose. leaving oil in the cylinder; In more than one. (Might check to see if you have oil in the Radiator.)
Turning the key and the Starter engageing the fly wheel with the aweful sound of the pinion gear not turning the flywheel "Click" - could be motor froze up.
Or you threw a Rod, Baring - making the cars motor cease up.

somethings to check to see if this is whats going on or if im even way off base here.. give more detail about the problem so it can be solved. do some checking of your own to figure out where the problem really is.
Start with checking to see if the timing belt is intack.
locate the starter and check the wires to make sure they are in good shape.
ummm -- might try to move the crankshaft with a very large socket to make sure you can feel the motor turn. if all thats going good for you, then on to more steps. let me know what you find out.