It depends on where you are staying at Disney. There are 2 locations on Irlo Bronson (Hwy 192). There's one near the Animal Kingdom area, and then there's one that's cloer to Pop/AoA/CBR.
Osceola/Kissimmee (near Animal Kingdom)
US 192 & Silk Road
7878 W. Irlo Bronson Memorial
Osceola/Kissimmee, FL 34747-1738
Located off US 192
* Bus & RV Parking Available
(407) 390-1190
*Note* when you leave here, you can go left and turn on Sherbeth Rd which takes you to Osceola parkway which is Disney property. If you are not allowed to turn left, then take a right and turn right on Black Lake Rd. That dead ends into Sherbeth Rd; take a left. Easy to see if you type the address into Mapquest.
Kissimmee (closer to Pop area)
I-4 , Exit# 64A
I-4 & US 192
5400 W. Irlo Bronson Memorial Hwy
Kissimmee, FL 34746-4709
Located off I-4
* Bus & RV Parking Available
(407) 396-6521
There's one on Orange Blossom Trail, but that's out of the way. I think all the other locations you would have to head above Universal in the opposite direction from Disney, so the 2 I listed are probably your best bet.