No school has a one week course, however if you go to Recoleta and go to the visitor's center (tourist information booth in recoleta park) they can tell you places where you can practice your spanish, some youth centers, some pubs or some libraries or museums where they have special events for tourists to practise their spanish.
Hi, I would recommend El Pasaje Spanish; it's a small school, with really cool teachers and tailor made classes. I studied there and not only I found great teachers, but also I made very good friends (students, teachers and owners, who were all young and really fun to be around). You can take one week classes there if you want! They have individual and group intensive courses.