Please tell me the website or link from where i can download my WIFI driver. It's showing compatibility issue with this operating system.

Can you be more specific / which dell notebook model or even better yet: there is a "service tag" number on the bottom of the machine. If you can post that I can tell you exactly which WiFi card you have and where to obtain the proper driver.
-Davis

This is the Dell download site. As you can see your service tag as wfor1pilot alluded to should get you the drivers you need.