Osceola parkway is Exit 249 on the Florida Turnpike.
Heading West on the Osceola, they will pass under I-4 and then about 1 mile later they will pass under the Walt Disney World Entrance Archway on Osceola.
The next intersection is Victory, continue on Osceola through it.
Look for a sign indicating "Magic Kingdom Resort Area", it will point to a right exit. This exit will drop you onto World Drive - which proceeds to the Magic Kingdom parking toll booth.
Get into one of the far right lanes at the toll booth (but not the bus lane at the very right hand end)
At the booth, tell the Cast Member that you are checking into the Polynesian.
You will proceed straight forward (not off to the left - that's Magic Kingdom parking)
At the first stoplight, you will turn left. It is well marked that it is the direction to the Polynesian.
You'll pass the Kennel, then the Ticket and Transporation Center, then the Guest Dropoff Area. Then, on your right, you will see the entrance to the Polynesian.
Hope that helps.