Integration with other community system

[lovegreen]

I originally posted this at vBulletin.com, but they told me to ask here, so I am hoping for any comments/suggestions to this.
Thanx!

-------------

I am running a rather large online community, and we are currently in the process of changing to a new system, because of many problems with the old one.

I am considering using vBulletin as the forum for my community, but have a question in that regard:

Is it possible to integrate vB with another community-system in such a way that you only have to log-in ONCE (to the existing system) which then transfers user info to the vB forum (which creates a new vB user account if that user doesnt exist yet), thereby making the trasfer from my current system to vB "transparent" to the user.

UltimateBB has a system called 'oneCommunity' that does this, so you don't have to register twice to use say a chat and uBB-forum, but they are pretty pricey.

I've searched this forum and have seen suggestions to similar problems. The suggestions were that you make vB handle you central login/myPages and then trasfer information to other apps as needed.

I'm afraid to use this solution since my community reaches +10.000 active users (on the entire system = forums, chat, profiles/mypages and online games) in peak hours, and I am afraid that vB will be unable to cope with this. I've seen post that claim vB starts having problems at around 3.000 active users.

Our forum part of the community only reach about a maximum of 1-2.000 active users, so I'd rather have a custom made central login/mypage and then transfer the login/userinfo to a vB forum.

Can I be done? Has anybody done something similar?

Hope to hear any suggestions, since I'd love to use vB and it's many sweeet features!