Delete invisible Folder in Vista

That file has a name, even if you can't see it. Open a Command Prompt
window (cmd.exe). At the prompt, type:
dir /x

That should show you all the files and folders in that directory. The one
that you named (alt + 255) should appear with no name in the normal list of
files, but the column before that should show it as "0A00~1". That is the
Short File Name, also known as the SFN . Now use REN to
rename that:
ren 0a00~1 newname

after this you can delete the folder