How do I remove old computers from the Network folder in Windows 7?

"Another thing to try is clearing the DNS cache:
Open the command prompt in administrator mode and type ipconfig /flushdns and reboot.

If it's your router that remembers these ghosts, it might have a configuration screen
that will let you get rid of them·
Otherwise, reloading factory settings might do it, but which I caution against.
You might try to reboot your router if haven't done so already, then reboot your computer.

If all else fails, the ghosts will not stay there forever.
Just wait thru the timeout period, which might be something like 30-60 days."

"This may not work, but it's worth a go until someone with more knowledge comes along:
Go into the Network and Sharing Center, and click Change advanced sharing settings. From there, drop down Home or Work (assuming that's what you're using), and then change the Network discovery option to off. Save the changes and then have a look to see if those computers disappeared. Make sure to hit refresh or F5.
If they did go away, you could probably turn network discovery back on.
Like I said, it may not work, so don't get mad at me... ;)"