Cookies and Sessions

Allo, I seem to have run into a couple of problems with a project I am currently working on. First one is that the project has a login feature that tracks the user using cookies. The client alas has a desire to have multiple sites and have the login to other sites in his group seamless (in as much as he would like no additional logging in). Since the login feature uses cookies this requirement isn't quite fulfilled... ok, let me be honest, it ain't filled one little bit! The one thing I do have in my favour is that all the sites (at the moment anyway) have the same SERVER_ADDR. Is there anyway I can set a cookie using and IP Address rather than a URL. I have tried this with little success (setting the path to ""). As a side note, I would like to be able to use sessions more but I am running into some (very) peculiarities. I have a library which starts the session and then I regester variables till my heart is content. Trouble comes when I want to view them in another page... nada! If I do a 'session_is_registered' on the variable it returns true so it seems to have the sessions set up just not updating the values.. not sure. Now I can set up small two file proof of practice examples but when I integrate into my existing project code I suffer from all manner of wierdness .. the most notable being the complete lack of persistence. I know it is a bit of a shot in the dark in as much as I have provided little in the way of diagnostic information, but would any of you bright bunnies be able to give me some pointers as to what I might want to look into to get more of a clue as to what is going on? Cheers for any assistance Kevin @TheConfused