You might have noticed a MSOCache folder in the root directory if you have selected the option to view hidden folders in Windows Explorer. Microsoft Office creates the folder during installation to cache files that are needed to install Microsoft Office.
The folder is not needed to run Microsoft Office and can therefore be deleted safely. It has to be noted however that Microsoft Office will first use the files from that folder if the user activates the repair option. A deleted folder means that future repairs and installations need the Office installation CD or DVD.
Here is how you check if the MSOCache folder exists on your computer system.
Start by opening Windows Explorer. Select Tools from the top menu and then Folder Options. This opens a new window. Switch to the View tab and locate the Hidden files and folders section.
Switch from "Don't show hidden files folders or drives" to "Show hidden files, folders and drives". This is enough to see if the MSOCache folder exists on the computer system.
Update: Select View > Hidden Items in newer versions of Windows which display a ribbon at the top so that you don't need to dive into the folder options anymore for that.
Open the c: drive in Windows Explorer and see if the MSOCache folder is there.
A right-click on the folder and the selection of properties reveals the size of the folder on the disk. This can be anywhere from 430 Megabytes if Office 2007 is installed to more than 750 Megabytes for Office 2010.
Select the folder and hit the delete key if you want to delete it. Deleting the MSOCache will require the Office CD for the following operations:
Detect and Repair
Maintenance Mode Setup
Installation of service packs and patches
Make sure you have the installation CD or DVD before you delete the folder. An alternative to deleting the folder outright is to back it up before deleting it. This way you can restore it if the need arises.