Logging in to vbulletin using external form

[dionsis]

Ok so i have an external site and want to use the login that i use for the main site to log vbulletin in when they log into the main site

i would also like it if they logged into vbulletin that it logged them into the main site

also the logout function would be nice to have synced as well

basically im assuming i have to point these variable to the vbulletin files but im not sure what i should be doing and not sure how to do the vbulletin plugin that would point the variables at the main site so that no matter what login everything works

any help would be appreciated