what the difference b/w polyurethane and solid motor mounts?

Solid mounts are exactly that; solid. They transmit the full power of the engine through to the chassis, and you'll feel everything from it. Polyurethane mounts are similar to the stock rubber ones, but they offer a little more insulation between the engine and chassis than a solid mount would, while still being stiffer than a stock one. Were it my decision, I'd absolutely go with a poly mount over solid anyday on a street car.

i just got stock replacements. from what i have heard, stay away from the soild mounts. they are more for an all out track car.

I also would not use solid mounts on a stockish street car, and I would be REAL hinky about using a solid trans mount.