guidosmom
I was forced to quickly learn Spanish when I was younger. I was sent to Spain to live with a Spanish family for a summer when I was 14. I took classes in junior/high school but nothing compared to being forced into the language 24/7. I came back after 2 months speaking fairly well. I went back every summer throughout high school, then moved there for a year.
Since moving to a country is not usually practical for most people, I think the best way to learn is to immerse yourself in the language as much as possible at home. Take a class, read books, listen to Spanish music (children’s songs are great), radio programs, tv (dvds are good, most you can watch in Spanish), subscribe to Spanish podcasts, and try to meet Spanish speaking people to practice. I have friends who have learned languages through the Seattle Language Academy and speak very highly of it:
http://www.seattlelanguageacademy.org/
I know the Seattle Public Library used to have a book club for people trying to learn Spanish as well.
Good luck.