Question: Recently I downloaded ubuntu 13.04 (iso). Now after extracting the iso file and running wubi - it says downloading required files though I had already downloaded the iso file (794 MB). So what to do now?

Answer: 
wubi in 13.04 is not in a releasable state. You have to install Ubuntu 12.10 through wubi and then upgrade to 13.04. follow this [steps](http://schoudhury.com/blog/articles/install-ubuntu-13-04-with-ubuntu-wubi-installer/)
If you're on Windows, or even on Wine you could also try Unetbootin or LinuxLiveUsb.

I tried both of those for the first time yesterday, both were remarkably easy to use and did the job perfectly.