Integration with existing custom pay site

[BretttT]

I have an existing pay site for which I have purchased vBulletin as the forum application.

Since it would be ridiculous to have our users log in twice we need to:

1) Automatically create the vB user record when someone signs up for a membership on our site.

2) Set the proper cookies/sessions/whatever so that when a member logged into the site goes to the vB section they are already logged in.

Step 1 was pretty easy, but step 2 is giving my coders ulcers. I've done searches here but the vast majority of posts are for intgration with off-the-shelf packages.

If anyone here could point me in the right direction it would be appreciated.

Thanks,
Brett