While installing Vista, Windows stores any existing installation of Windows on the install partition in a hidden folder called windows.old. This folder consumes lots of disk space.

Deleting the window.old folder using the disk cleanup wizard

• Go to start >> in search box Type: disk cleanup

• Then Press enter

• choose "Files from all users on this computer"

• Follow the instruction and choose the option to delete the windows.old folder
Deleting the windows.old folder manually

• Click start >>Type: cmd

• right-click it under programs

• click Run As Administrator

• Change the directory to the windows.old folder (e.g. cd c:\windows.old)

• Type: takeown /F . /A /R /D Y > NUL

• Type: icacls . /grant:r AdministratorsF) /T /L /Q

• Type: cd ..

• Type: rmdir /S /Q windows.old

Ensure you close any explorer or command windows that are looking at or in the windows.old folder. If you do not, you will get an error while performing this step.