Peter from Kerrville, Texas writes:
My system runs Windows XP, Service Pack 3. In the “Windows” directory there is a sub-directory labelled “Installer”. This directory is very large (2 GB) and contains many .msp and .msi files. My question is can any of these files be deleted in order to regain some disk space? Thank you in advance for your help and answer.
The installer directory contains software patches and installers which may be critical to removing or updating certain pieces of software on your system. It is not a good idea to remove the files unless you know for sure they pertain to a program you no longer have installed. The good news is, if you’re not running Office 2007, you can use an older utility from Microsoft called the Windows Installer Cleanup Tool. It will clean out the installer directory of packages that are no longer needed or valid.
Since the tool is no longer supported by Microsoft due to compatibility issues with Office 2007, you’ll have to download it from a third party. You can download the tool from Softpedia by clicking here  then clicking Softpedia Mirror (US) [exe].
Double-click the installer and follow the installation prompts. Once you have installed the tool, open a command prompt (Click Start, Click Run, type cmd.exe and press enter.) and type msizap.exe G! to clean out your installer directory.
P.S. Though I’m usually big into saving as much hard drive space as possible, saving space in the Windows folder is one exception I make. While this tool does what it says, I always allow my Windows folder safe haven from my hard drive space worries. It’s quite difficult to figure out what packages might be associated with or used in future for some application. A few extra gigabytes on a modern hard drive won’t hurt.