Need Single sign on solution ?

Hi All,       I am doing my site user authentication through LDAP server and my company has 3 more sites with different technologies and they are also doing user authentication through LDAP server. Now we want that when user logged in my application 1.domain.com then user also logged in other application 2.domain.com and 3.domain.com. Please help me out. I will be so thankful to all of you?

If u r saying bout session or cookies please give some code example or detailed description.

Thanks & Regards, Varun Goel