i have created a login that supports VBulletin, however, i have not done the cookies part.
it's not a 1-2-3 process i don't think though.
But look at the VB files.. and also very important, what version of VB are you running?
beucase the whole login process changes drastically from 2.30 to 3.0 Beta 4...
i upgraded to 3.0 Beta 4(really great btw) 2 nights ago and my home login got really screwed up... i had to fix that one.
i suggest upgrading first.