Hi Tamara,
What great timing you have with this question! I, too, had recently heard of the Muzzy DVDs and looked into them on the following site http://www.early-advantage.com/.
From the website, it appears that there are a couple of options before purchasing the DVDs: 1) the site mentions "trying" Muzzy free for 30 days, and/or 2) you can possibly find it at your local library.
I chose to check with my library and, although they DIDN'T have it, they were able to borrow it from another library.
Since we just received it a few days ago, I don't have any feedback to give on the program itself, or its ability to teach my little boy Spanish (he's 25 mos old). But, I did learn that many libraries carry it, so hopefully that helps you!!
Good luck!!
EDIT: You may also be interested in putting your twins into "spanish playdates" activities, which I also learned about when researching ways to get my two-year old exposed to Spanish as often, and in as many different ways, as possible. I spoke with Karina Z. (www.bilingualpals.com) at ###-###-####, and she told me that she anticipates starting a set of "playdates" activities starting in June this summer.