I'm currently a college student in the USA. I'm majoring in computer science, but also minoring in Spanish. I speak Spanish pretty fluently as I've studied it for five years and spent last summer in Madrid near Sol. I'd really like to be able to return to Madrid this summer but I won't be able to unless I find some type of part time job to cover living expenses while I'm there. I'm still a student and figure if I had some type of income while there I’d be able to spend most of the summer in Spain. Is there much of a chance of me finding anything? I've heard that some tour agencies want bilingual English/Spanish tour guides, but I'd probably need to be more familiar with Spain's cities/history to do something like that. Have any suggestions?

I don't know about mainland spain, but in the canary islands for example, in the tourist areas, they are always looking for bilingual people as PRs for the various hotels, timeshares and restaurants. Possibly it is similar in Mainland Spain?

Im hoping to do just what you talked about this summer. I spent last semester, and summer in spain, and just have to go back!!
Iv done a lot of searching and got some ideas, but so far, the best thing Iv found to do is get with an organization or group that will help you organize the entire thing, get set up with something before you leave the USA, and get proper visas and stuff so that it is legal. I joined AIESEC for that reason. Im still entirely open to other options though, so let me know if you find anything out! If you do a search under this forum, you can probably find my other posts on this kind of thing (sorry MM, i dont know how to do that linking thing haha).
Good Luck!
Kelly