Choose a Digital Certificate Blank!!

My companies web site uses Certificate Authentication for identity users, the Certificate is issued by CA to end users. The web site allows a user to login in to the site after inspecting the certificate . In my case i am running windows vista and when i load my companies web site and click on SSL option that i get "Choose a Digital Certificate" dialog box but i don't see any certificate listed. I have tried importing the Manually and have added the site to a security zone but no luck. Is there anyone who can help me out?? I want to gain access to my companies web site as soon as possible as i have lot of pending works to do.

As far as i am aware Windows Vista requests certificates using different cryptography compared to other operating systems. If you will leave the default options, then you wont be able to use certificates for web authentication. I want to know if there is anyone in your company who might be accessing the same website form windows vista. If yes than better contact him and ask about the tweaking he might have made or better contact your company IT department.