I started captioning about a year after I began CART. I had applied to Caption Colorado and then got hired in late November. I know there's a lot of controversy with them regarding pay, but I like my schedule (very important to me now with a 4-month-old) and the people.
I took captioning classes and did an internship in school, and then when I did CART, I would just practice to TV (start with the weather -- it's easiest, or local news. Then move up to national news and something like "Oprah" or any talk show you like. And of course anything fun :)
Captioning and CART are pretty similar with just a few differences. I would also look into one of those boot camps, if you can afford it, or an intro to captioning class.
Hope that helps some! If you have more questions, let me know.
P.S. Portland is a great city. We have relatives four hours south and fly to PDX. In fact, we're going to see them next month with the baby.