Is it safe to delete from C:\Windows\Installer?
The Windows installer folder is getting to be 8 GB. How do I shrink it?
It stores copies of the MSI files used by Windows Installer to make sure you can make changes without requiring the installation media.
If you clean it out, you run the risk of not being able to change or remove installed applications, but YMMV.
Try using the excellent, free CCleaner - it can free up a lot of useless junk on your hard drive.