Check and improve code I wrote for securing an ASP page accross multipul domains

I have written code to allow asp cookie sessions to be maintained accross multi domains. The code works by relying on timers and cookies being set on leaving the site and arriving at the new site. The user database is a standard vbulletin database using MD5 and salt in a mysql database. I use the same MD5 authentication as vb, but in ASP not PHP. I have created a session database which has a child / parent relationship that needs to be maintained, where the logged in domain is the parent, and the visited domains are the childs. I have tested it and it most cases it works. Sometimes it does not work, and I cant seem to see why. It does not always work behind a PROXY server or a company network. The areas that need improvement are the way the sessions is delt with if two user have the same useragent and ip address. I can provide a visio flow chart, and a sample of the rows of the 3 mysql tables that are required. This needs to work along the same lines as I have written it using cookies and times and **NOT** session varables. I dont think this is a major piece of work, just need somebody who has a bit more experance in securing ASP sites. I want a system which I can 100% trust, that will work purely on cookies and timers using VB and mysql. I am not sure how I am supposed to work on here, but I can provide the visio and code before any undertaken is given, so people will have more of an idea why this works. I am not very good at ASP, and any good coder will find my efforts fairly basic. Graham ## Deliverables My final requirment is to simple be able to hop between multipul domains I have maintaining a cookie based session, stuck together using a mysql database. I am fairly happy with the registering, and logging in part of the site, it is the session checker that has issues. I wont to be able to have two users logged in, with the same useragent and IP address without have any issues or effecting each other session. All of the privledges and registeration I can probally handle.