My laptop is running Vista 32-bit at the moment, and the C:\Windows\Installer directory is over 5GB big! Not too pleased about that, I set about trying to find a way to either delete it or move it to my bigger D:\ partition.
Using it, I was able to move the whole folder to the D:\, and then use the command
junction C:\Windows\Installer D:\Windows\Installer
to trick Windows into thinking that the folder is still there.
Something I’m used to doing on Linux, but not Windows.