Multiuser System with Sessions

Hi, I'm building a multiuser system with PHP. It appears that session data is getting overwritten with the latest users information. The site is hosted remotly with a virtual host. The problem only seems to occur to people inside our building (i.e. two people here login to the system with seperate logins). Example: User 1 logs in, session data is: UserID = 1 DescriptionEntered = No QuestionsVisible = No QuestionsRanked = No User 2 logs in, session data is: UserID = 2 DescriptionEntered = No QuestionsVisible = No QuestionsRanked = No Once User 1 refreshes the page or goes to another page User 2's information shows up. So it appears that the last login is being set for the session. I've gotten my host to look into this. From their end they login with the 2 ids and the session data stays completly seperate. Our building accesses the internet through a DSL connection. Would that cause a problem? Any ideas are greatly appreciated. Anson