Synching logins from main site to Vbulletin forums

[mymint]

I am working for a client that wants to utilize Vbulletin. I did, however, have a question about creating synched logins from the main site to VB or vice versa (we don't want folks to have to register for two accounts). My questions:

1. What's the best option/mod for doing this?
2. What's the best way to get it going?
3. Is there a different option available? In other words, what would make it easiest for not having to do extensive modification of the code for VB? I believe there is an option for making the main site utilize the VB system w/o such modifications.

Thanks, in advance!