Connecting nokia 5233 as a modem to PC

Hello,
I want to use internet via my nokia 5233 (using airtel mobile office)on my computer with windowos XP,I have installed nokia pc suite sucessfully. But when I connect my phone through Data cable.Go to PC Suite> connect to internet,it automatically shows connecting but after sometime A message appears on the screen "failed to connect to internet" & my connection is not established. I have airtel mobile office setting on my phone & also able to use internet on my phone.
It would be nice if a reply is given back.
Thankyou