Create a Task with Webdav

Hi,
Am trying to create a task in MS Outlook using webdav.... But its not
working at all...
I can create the task in DOT NET application... but when I use same code in
Web Service then it wont work...
I can create the appointment using Webdav. Its working very fine... 
 
 
Will you guys provide me any type of help in that... Please help...
 
 
Thanks and regards,
Nitin.