how can i block website on my computer

In windows xp just click on My compouter then click on drive letter where windows loded then go to windows\system32\drivers\etc
there you find host file open this file in notepad
at the end of file u will get entry

127.0.0.1 local host

under this write which site u want to block
for example you want to block yahoo.com

127.0.0.1 www.yahoo.com

now you can't open yahoo.com now
like this you can add more site here which you want to block

thx