[Zachery]

There is a similar thread search built into the software, however it only compares the title, and it only works after the post has been made.

If you wanted to do something like this, from scratch.

When do you check if the post/suggestion matches? What are you matching it against?
Do you wait until its all done and they've wasted all this effort?
Do you LITTERALY block them from posting if something similar has been suggested?
How would you feel as an end user if you took a HUGE amount of time to write something up for it to be completely blocked?

You could (if done wrong, but with the best intentions) hammer a forum's database to death by trying to do lots of searches.

Seems like active moderation from your staff, and clear enforcement of the rules, would go a lot further than trying to auto program something. You could also moderate new posts and make sure that the new posts don't match any old posts as well, by using both the similar thread search and moderating new posts. The new topics will be moderated, but have their similar thread search run.

Might do what you want.