Java.net.UnknownHostException Urgent

Java.net.UnknownHostException

I got this exception in my system, when trying to fetch the contents of a web site for example, yahoo.com. But the program running in another system fetches the website contents successfully. In both the systems JDK version is 1.2.2 . But I don't know why this exception occurs in my system only?.

Is there any solution?. Please inform me if you know the solution. I will be very thankful to you. This is very urgent to me because I have finished all the coding for a project. Now I found that the program is not running my system and giving this exception.

[615 byte] By [dearamjath] at [2007-9-26 4:37:20]