contact form target attribute

Again, dunno for sure if this is the right place to ask but this is the problem:

I need to modify the target drupal's contact form (it's for a somewhat weird theme with an iframe somewhere... just don't ask why, it's just got to be this way!.) and don't know how... gues I should overwrite in template.php a fucntion that generates this form but I don't know where to find this function or... maybe that's not at all how to do it...
Hope someone can help me with this.