Best Way To Merge My Existing Custom User Database With WordPress?

I'm sure this has been asked before though I can't seem to find a clear answer or clear direction on how to handle this. Would appreciate a point in the right direction.

I have an existing custom website/web app with about 7,500 current registered users in the database and I want to add a WordPress help forum. I have installed WordPress and a Q & A plugin in a help dir on my site. What's the best way to handle not having to use the wp databases?

I have played around a little and wrote a plugin that pulls my session/cookie data userinfo on the WordPress pages, can I somehow manually set or override the existing wp user_id and other vars so that when a new entry in entered it corresponds with my current database?

I'm also assuming I would need the register link to be changed to my site reg page as well as update WordPress somewhere so that it pulls names/emails of entries userid from my database.

Is this even the right way to handle this or is there a better way?

via Chebli Mohamed