when i copied my deployment descriptor file in WEB-INF folder....and then opened my form.html.....it displays file not found
As you surmised, this indicates that the server is not recognizing the existance of your web application. There are plenty of things that can cause this, from incorrect names of directories to XML errors in the deployment descriptor.
What is the directory structure for this new application?
How did you install Tomcat - as a service or as a regular application?
How are you starting Tomcat?
Are there any error messages in the log files
Bill