In order to keep your documents organized, it makes sense to keep them in the same location on your computer. I recommend storing them on a second hard drive—internal or external—in the event the drive with your operating system is damaged.
It's easy to specify a default save location for your Mac Word 2008 files. All you need to do is follow these steps in Word 2008:
1. Open the File menu
2. Click Preferences
3. Select File Locations
4. Choose the type of file for which you would like to change the file location. In this case, select Documents
5. Click Modify
6. Navigate to the folder where you'd like to save your documents
7. Click Choose
8. Click OK.

