Could any body help me with some info on working of ASP.net with Win-XP ?

Question

Hi, I am finding a difference in working with my site developed in ASP.net and C#,SQL Server. That is when I accessed the same site from Win-2000 , I am able to work with the functionality available within the site..but when I accessed the same site from Win-XP machine, I am loosing some of the functionality like impersonating the user, etc. So, could anybody give me some information regarding the same issue depicting the differences between Site Access from WIn-2000 n Site Access from Win-XP ? And even I am wondering about why the system is behaving like that ? Note : Used same settings for Internet Explorer for both Win-2000 n Win-XP. Thanks and Regards, Madhu.