Bourbon vanilla is a type of vanilla. There are two main types of vanilla, and one other that is harder to find. Madagascar Bourbon vanilla comes from, guess where, that's right Madagascar. Tahitian vanilla comes from Tahiti. Both taste slightly different. Tahitian vanilla has a slight licorice flavor that Madagascar vanilla doesn't. In addition, there is Mexican vanilla, but that is a strange area. Some mexican vanilla extracts are legitimate, however some are cheaply made fake vanilla extracts that have coumarin in them. Coumarin is potentially bad for you, as it can cause liver and kidney damage, and a derivative of coumarin is used as a blood thinner. If you want Mexican Vanilla extract, get Mexican Vanilla Beans and make your own.
FYI, the Bourbon in Madagascar Bourban Vanilla comes from the Isle of Bourbon, where the french first planted vanilla orchids. That isle is now called Reunion with a little accent over the e that I don't feel like figuring out how to type.
As for making vanilla. I bought a 1/4 pound of vanilla beans on ebay, split, scraped, and soaked them in Absolut vodka in an old wine bottle. I shook the bottle every few hours for the first few days, then went to once a day, then once every few days, then whenever I thought about it. After 6 months, I had a beautiful brown liquid with a strong vanilla aroma and an amazing taste that I use in anything that requires or deserves vanilla. I simple strained it through coffee filters and poured it into some 2 oz. glass bottles I bought online.
Its a relatively inexpensive project that yields great results.
As for siduri's question. I think using a completely neutral spirit would yield better results, however, as vanilla extract is usually 35% alcohol by volume, you'll have to add water to your final result before bottling or using. I have considered making my own limoncello for a while, and will be doing so sometime in the near future. In fact I want to use lemons, oranges, and key limes to make a few varieties.
Here's a interesting suggestion. When I was in Walt Disney World a few years ago, I had an Italian Margarita. It consisted of freshly squeezed lime juice & simple syrup (as in a good traditional margarita), and instead of Tequila and Triple Sec, it included Grappa and Limoncello. It was much smoother and better tasting than a normal margarita. Worth trying.