Power To Weight Ratio

Can someone explain the whole power to weight ratio thing. I wanna compare cars but im not sure how, the only things ive heard of are that its the power or torque divided by the cars weight, but whats the number mean if your comparing it? Also I heard sumthin like a car with 250hp and 2000lbs, could keep up with or would be around the same as a car with 500hp and 4000lbs. Yes I know there are alot of facotrs like driving suspension, weather and all that but wats the basics, and how does rwd,fwd, and awd change things?
*Number Edit*

first off i assume that you meant 250 where you said 2500. anyways, it is generally so and so pounds per horsepower. like a 2000 pound car with 250 horsepower has 8 pounds per horsepower. a 500 horsepower car that weighs 4000 pounds also has 8 pounds per horsepower...

That's the general idea. For example, a Lotus Elise, which has 190hp but weighs under 2000 pounds can keep up with and M3, which has 333hp but is much heavier.

the general idea is hp/weight.
fwd,rwd,awd in theory will differ at launch fwd will tend to spin tires because of the weight transfer from front to back,rwd will have an advantage in this case and awd should technically dominate but then you think,all that power is being distributed to all 4 wheels(awd)and that most likely has a negative effect,because you are distributing the same amount of hp to 4 wheels instead of 2.
dont quote me on this because there are instances where this "theory"might be proved wrong

i meant weight/hp

yeah that's exactly it, u all have it. guess we could kill this thread now. :lol2: :lol2: :lol2: j/k