when you two users access a web part page, ASP.net creates two seperate sessions for them. it means they are running their stuff in their own thread. ASP.net processes runs in seperate threads per requests etc. You do not need to implement seperate threading
in a web part. Seperate threading would be required when you write some timer job type code, when there is only one instance running to perform a job and you want to process multiple things into seperate threads. It is not applicable to web parts. I hope you
get the idea.