Single Sign on

Hey,


I am just looking for a option to implement single sign on.  I have two domians www.domian1.com and www.domina2.com.  both using form authentication.


Currently for the sub domain we uses encrypted cookie bases solution .. (sharing the cookies) ..i guess this won't work since sharing of cookie will be an issue ...


Can any one suggest a  better way to implement this ( appreciate responses from some body who implemented the solution for a large internet website)
...