URL Blocker..

Hi,
I am connected to internet through cable modem and have dynamicIP. my problem is that i have a set of URL’s which i want to block from my computer. If i go for any firewall software or parential control software they are limited and they have their own database for the URL’s and their own category, i am unable to manually insert any URL’s. That does not solve my problem. So any of you know any software through which i can block those URL’s(Atleast 50 url’s). SO can anyone suggest any way so that i can block these URL’s.

Regards.