how to show sitewide most popular post

right now i’m using wmu-sitewide tags to collect latest posts on main site front page.
1. now i want to show several most popular posts for some time (like for the last 30 days). Popular by most commented. Is there any plugins/widget to accomplish that? right now i’m using wordpress popular post widget, but it return false result, since it dont count the number of comment of posts in child site.
2. is there any plugin to show several latest comment site-wide?
3. is there any plugin to show several most active site (on post published) for some time?
my network using wp3.0 and the main site using themorningafter theme