There's some really great advice already posted here. As for letter vs. e-mail, I'd recommend a very formal letter, sent via overnight. In my opinion, there's a sense of substance and professionalism in a written letter that you can't replicate in an e-mail. I would make the tone upbeat (I remain excited about the possibility of attending SW, my first choice, etc), but dead serious (Because SW is my first choice, I would like to provide you with any letters, statements, demonstration of my interest, etc that might improve my chances for a favorable decision, etc etc).
Further, I'd be direct in all correspondence - written, verbal, in person. Make your favorable impressions on people who truly make a difference in the outcome. If I were calling, I would try my very best to speak with Anne Wilson. I'd have talking points prepared -- like the things I've been up to since I last corresponded with the school. I'd ask very specific questions, and would check in advance to make sure that the answers can't readily be found in their viewbook or on their website. From this point forward, you're a sales executive. Your marketing materials have already been mulled over, and they've got you in a holding pattern. Time to follow up strong. Bring your self-confidence, maturity and enthusiasm for SW to the forefront. This is why I'd highly recommend a visit. But if that's not possible, then phone calls and formal letters are the next best thing. Following up your letter with an e-mail to check on its receipt is a good idea -- yet another opportunity to express your interest, while having a good reason to write.
Another suggestion for where e-mails may be effective: head of the department or program you're most interested in, or a professor whose course(s) you really want to take. I'd recommend the same tone, give them the ultra-condensed version of your story (1 paragraph max), and ask them what they would recommend you do in order to enhance your chances for admission.
Best of luck!!