Encourage Posting

[ktp101]

i have a few users who come onto my site solely to use the shoutbox, and its pretty annoying, i want a way that means people have to make a minimum amount of posts everyday to gain access to using the shoutbox, or a daily minimum to promote them to a different usergroup but for it to reset at midnight or whatever time i set dropping them back to the original usergroup.

i hope this
1. makes some sort of sense
2. is possible

any takers or advice?