Just curious, so you press on the gas and the brakes at the same time, then what happens when you let your foot off the brake? Does the front end of the car lift off the ground for a while? Sort of like a drag race start? This is all done with the automatic set to D? Or do you change gears rapidly from neutral to D as part of this?
Is it called a "brake stand" c/c the car sort of stands up like a dog begging for a bone for a little while?
hmm .. so the problem now is the car won't move in D, even when you press on the gas? But the speedo shows 20 mph and you hear weird sounds? hmm .. well, that doesn't seem like what you'd call a good thing. If the speedo didn't move up like that, that might be you got lucky, and just the brakes are locking up. But w/the speedo moving, that comes from the transmission output shaft or governor, and would indicate a problem with one of those parts. There's some chance it is just the transmission clutches have gone south I suppose. Even so, it's probably transmission out of the car time. Best to take it to a transmission shop for a proper eval.
hmmm .. did you look under the car and see if there's anything looking not right, like the end of a drive shaft laying on the ground. It's possible the transmission output has somehow become disconnected from the drive shafts perhaps. Maybe it is just the differential part is the problem.