Archives related query

Hello friends,
I am having a query, Please if possible help me to resolve it. I wanted to check in archives.php page that, if somebody is trying to access http://smsite/blog/uncategorized
I want to block it, I wanna redirect that person to Some other page. If he tries to access http://smsite/blog/uncategorized/some_post
Then only i want to give access. Please help. Thanks
Regards,
Mandar