Blog

I was wondering if there was away to stop members from posting in other members blogs? Maybe have a comment box for comments that appears in the blog. Like in the post it shows up like this..
[IMG]http://i54.photobucket.com/albums/g101/Dollieblitz/comentblog.gif[/IMG]

When they click to comment they have a button kinda like this [IMG]http://i54.photobucket.com/albums/g101/Dollieblitz/comment.gif[/IMG] and some how rig it up so when ya get a new blog comment, it sends a pm?