Is there a hack by which i could integrate 2 sites together..

for e.g. take i have x.com and started a new site y.com so i want my existing members on x.com to have a account on y.com ... i have a option to have pre accounts for them installed on y.com

but want to know is it possible for me to add a banner link on x.com redirecting ppl to y.com and access y.com without registration... prob the link makes the member visiable as x.com guest on y.com a new usergroup who have previlliges to access the site without registration.

2)Could someone guide me on how to transfer all my existing members from x.com to y.com

maybe you should look here (Multiple Forums using a single user table).