Private Messaging - PM Categories or Private Forum?

[himerus]

I'm looking for something similiar to this:

I'm working on integrating my frontend site with the vB forums in the following way: I need to have the ability from the main section of my site for users to contact a user that posted a project. I can handle passing the appropriate data to vB, however, I'm not finding anything similiar here that might make this possible...

I thought that either using private messages, this would be possible... just prepopulating a title, and assigning the PM to a category that was associated with the specific project they posted on the main site... The main feature to add here would be the category, so the user could easily manage thier PM inbox.

However, the problem with this is that then it will make it difficult for myself and other admins to monitor those PMs, which have certain posting rules... (like no email addresses, etc.)

SO my next idea was a forum like at vbulletin.com where it is labeled as "private"...

if I set it up this way, I think there would still be some hacking involved, because the thread starter would need to be able to see all messages posted, and the other posters would be able to see only thier posts, and the posts of the thread starter that were directed to them, not everyone elses...

This is a PM feature that is found on a bunch of freelance web development sites... I'm looking for the easy way to throw this feature to my vB with either PMs, or a private forum somehow....

Thanks for ANY advice on this!!!!