Joomla and vBulletin in the same directory

[BozzaJos]

Hello ladies and gentlemen,

Here is my situation. I'm running my site for almost 3 years now. With over 80,000 members, we are a pretty big community. Till now, my site consisted of a forum with vBAdvanced installed as the frontpage. I've always thought that vBAdvanced slowed our progress down and we were in need of a proper site.
For the past months, I've been working on a new site using the Joomla software. The new site has a separate database and you won't be able to login or register an account on it. First I thought to move the forum to a sub-directory called "forums". But now someone on vBulletin Forums told me that it's not such a smart and necessary move for the search engines because the urls will change and the ones who are already indexed won't work any more. He told me to just move the new site to the root directory, together with vBulletin.

My question is if this will work and if there won't be any complications and conflicts, having vBulletin and Joomla in the same directory. If it is possible, what are the things I should keep in mind and have to do? My knowledge about this all is pretty limited so I would need a detailed explanation if possible.

I thank you all very much for taking the time to read this thread and I hope someone here can help me out. Like I said, I am running a large community and I would like a little downtime as possible and the smallest amount of errors hehe.

Thanks again and take care,

Bozza