Time Machine is not working with me

I'm wanting to do a backup to a computer that is on my network. Time machine can not find the location by scanning. It has an option for manual setup but it is grayed out. Am I trying to set backups in the wrong application?

What is the external disk connected to? Is it an Apple Airport Extreme or a Time Capsule? I dont't believe plugging an external drive into another wi-fi base station will work.

I was trying to back up to another computer. A windows computer. I called apple about this they told me that this could not be done. Time Machine has to have the correct file system to backup to. So I guess this can not be done. Which I understand the file system issue.

The windows desk top that I have is backed up to Mozy. What I was trying to do was just add the Mackbook Pro back up to that pc to be stored off site. Guess this is not going to work. So back to the drawing board.

Why not just add the Mac to your Mozy account? You can back up more than one computer, but you do have to pay for it.