Accessing dynamic ip address of a system on internet

hi all,

can we use the dynamic ip address to identify a paticular computer on the internet .
is there a static ip address for a computer which have dynamic ip to connect to the internet
is an internet connection provider provides both static ip and dynamic ip to a computer

my need is to save the internet ip in the database and check while the user login to my website. if the ip address at the time of login and the ip address i the database are same then he can easily login. it works well with static ip addresses. but when dynamic ip is there then the ip is changing time to time. so i cannot keep it in my database

i am workig in vb.net and my aim to block the unwanted access to my website

please help as early as possible

thanks
grace

re: Accessing dynamic ip address of a system on internet

Not a good design, I suggest using authentication instead.