My best directions would be:
1) Hop in your car
2) Drive to Costco or Circuit City or
Best Buy
3) Purchase a basic GPS (<$100) - our Garmin Nuvi works great
A little tongue in cheek perhaps, but actually I am SERIOUS. A GPS is a godsend in Orlando. We borrowed one from a friend (another option to consider) for our first trip, and I was hooked. You can also rent one if you are getting a rental car, but the cost nearly adds up to buying your own.
Second tip if you go the GPS route is to download the custom POI (Points of Interest) file from Mousesavers.com. For IOA it knows a "back-way" that cuts 15 minutes off crawling through the front way.
Okay, so I haven't convinced you yet? From Vistana Resort, the easiest way to get to all things Disney is to Turn RIGHT as you exit the resort onto 535 (S. Apopka Vineland). Proceed to the first light and turn right again on 536 World Center Drive. As you pass under I-4 this becomes Epcot Center Drive and you are aimed right at the heart of Disney. Follow the signage from there to whichever park you are going to. Note: This is the best route to all parks except AK. There is a slightly faster way to AK, but not enough faster to have to memorize another set of directions. This is also not the shortest route to DTD, but due to heavy traffic on the shortest route, it IS the QUICKEST route to DTD. BTW - Don't forget to leave a trail of breadcrumbs. It is really easy to get TO the parks in the morning because of the great signage. There are NO signs pointing the way back to the resort, and you are tired, so that is the tougher route (yes I missed a turn in the dark on our second trip 'cause I figured I didn't need the GPS anymore - ended up halfway to Tampa...)
For the Uni Parks and City Walk, turn left out of the resort, hop onto I-4 East (more North than East, but they call it East). Follow the signs for Uni that start about 4 miles up. That will not take you in the "sneakret" way (only the GPS users get that - no seriously, I don't think I could find it again without the GPS), so plan for a bit of time to make the turn into the front gate.
Why do I always answer a simple question with a "War and Peace" sized answer? I do hope that helps!!