The answer to both of your questions is the south entrance by way of Grand Teton National Park. The south entrance is the shortest route between Boulder and Old Faithful. If your geography is as bad as you say it is you should get yourself a map so you can plot your route. You can also use mapquest.com to find your way.

I hope you plan to spend a few days in Yellowstone because Old Faithful is just one of many thermal features in the park. Lower Yellowstone Falls and the Grand Canyon of the Yellowstone are also must see. For planning purposes I recommend you spend at least 3 full days in the park to see the highlights. Be sure to get out of your car and into your walking shoes because there are miles of boardwalk and paved trails in the Upper, Midway and Lower geyser basins not to mention West Thumb geyser basin, Norris geyser basin and Mammoth Hot Springs. Be sure to stop at Canyon Village to see the Visitor Center and the displays there.

If you can’t get accommodations in the park or decide to stay outside the park you should consider the town of West Yellowstone located at the west entrance to the park. All things considered it’s the most centrally located accommodations outside of the park. I spent 4 nights in West Yellowstone last summer and 3 full days exploring the park. I would have liked to spend more time there but since it was my third visit and I also wanted to do some hiking in Glacier and Banff I limited my visit to 3 days. If you stay in West Yellowstone be sure to check out the Grizzly and Wolf Discovery Center located about a block south of the park entrance. Grizzlies and wolves are two animals that you are not likely to see in the park.

Whatever you decide to do, have a great time.