Ubuntu 8.10 not connecting to net
 

I have this problem where it shows that connection is established through ethernet(ADSL)and firefox doesn't open any of the websites.....

is your DNS configured?

Once you are connected check the output of the following command for your dns server entries.
cat /etc/resolv.conf

then try browsing to http://72.14.205.99 <- google.com

If you can browse by IP but not name then your issue is with the dns configuration on your machine.