i want to act my computer as a webserver..some of my friends located in other places, used that static address and visit websites(asp.net) hosted in my computer ?

You'll need an ISP that offers static ips. Contact your existing one and ask.

Failing that, Demon and Bytemark both offer static ip addresses for home broadband connections in the UK.

You could also use a service such as http://dyndns.com/ to get a hostname that you can repoint at your machine whenever the ip address changes.

for a static IP you will need to ring your ISP,

however to do what you want to, you do not need a static IP, you can use No-IP www.no-ip.org