Hi fullbite,
To begin with you've got three things that will almost guarantee your success in learning Spanish.
1. You are motivated to learn.
2. You have opportunity to use Spanish on a daily basis.
3. You have the need to use Spanish in meaningful communication. (IE: you must talk to someone in Spanish, who doesn't speak English, and the communication is important).
So to begin with, I think you've gotten off on the right foot.
You've asked about home study courses. I don't have any personal experience with any of them unfortunately. I have studied a lot on my own, but I haven't used any of the courses that are available.
Before buying one of the courses, you might check out some of your local public libraries where they probably have dvd/cd courses you can check out. This is especially true if you live in an area with a lot of Spanish-speaking residents.
I would also recommend you buy and read a book called "How to learn any language" by Barry Farber. You might also find it in a library. In that book Barry talks about a list of strategies you can use to learn a language on your own. If you get into it and use the strategies (to the letter of the law) that he proposes, you can learn a lot, learn it fast and you won't spend much money.
I would do those two things before dropping $100+ on a full-fledged course.
You might also like to read an article I wrote a while back on things you can do to learn Spanish.
http://www.tomisimo.org/blog/2006/la...eign-language/