I'm here (Berlin) from the USA now almost 3 months. My 10 week Intensive German Course has just come to and end and I may re-enroll and then apply for a visa but I'm a little confused about the visa requirements.

1. If I apply for a visa based on studying German in a language school is the visa only good for the time I'm enrolled? What if I want to take a week off here and there, am I considered illegal during that time?

2. Can I enroll in the Volksschule (sp?) to meet the visa requirement?

3. Do I need to prove that I'm financially stable (or supported)? In another thread I recently learned about the "Verpflichtungserklärung" but this seems more geared to someone staying with a friend/sponsor in Germany who is offering to take responsibility for the visitor. But I also met someone (also from the states) in my German class who says he simply provided a signed letter from his aunt confirming financial support. Is this consistent with anything official policy-wise? (He was fairly detailed in his recounting of it so I have no reason to doubt him.)