Hey guys --
The majority of the cholesterol found in our bodies is MADE INSIDE THE BODY. Very little of dietary cholesterol actually makes it into cells. That's why the "statin" drugs are so useful for lowering LDL cholesterol. The mechanism of action is that they act on the actual DNA strand to stop/slow production of the enzyme that converts fatty acids to cholesterol.
Just for clarity...
LDL ("bad cholesterol" -- low density lipoprotein) is a protein found in the blood that transports cholesterol from the liver to body tissues). It's labeled as "bad" because it's the protein that deposits cholesterol all around the body when there's too much. It has very little to do with your actual cholesterol intake, and more with your saturated fat intake.
HDL ("good cholesterol" -- high density lipoprotein) is a protein found in the blood that transports cholesterol TOWARDS the liver FROM the body tissues. In other words, it "cleans up" the extra cholesterol laying around your body and coating the insides of arteries. The reason it's "good" is because it helps to remove the excess cholesterol from the periphery.
Now, these two proteins are physically interchangeable -- what I mean is, HDL arrives in the liver to unload cholesterol for metabolism. It's size changes and a cellular tag is placed on the surface, now labeling it as LDL (the "density" part, whether it's high or low, just depends on chemical properties of the proteins)
When there are too many fats coming into the liver from the diet, the creation of cholesterol in the liver increases, thereby forcing an increase in LDL (to deposit this cholesterol away from the liver). This mechanism helps in short term survival after heavy meals (via evolution -- if the cavemen didn't have this mechanism after eating a buffalo, they'd all die of acute fatty liver and we would have been extinct by now).
So, that's the gist of LDL and HDL, I hope it makes a little sense, and I hope it makes things a little bit clearer for everyone!