1. Quit Illustrator.
2. In the Adobe Illustrator CS2 > Plug-ins folder, copy the current default startup files as a backup - Adobe Illustrator Startup_CMYK and Adobe Illustrator Startup_RGB.
3. Open these default startup files (Adobe Illustrator Startup_CMYK and Adobe Illustrator Startup_RGB) from the plugins folder.
4. Choose Window > Type > Character Styles.
5. Double click the Normal Character Style.
6. Select Basic Character Formats and choose the desired font from the Font Family pop-up menu.
7. Click OK, and save.
8. Restart Illustrator.
...other defaults can be set from these start up files, colors etc, etc...
...just be sure to have a backup of the originals, just in case...
Andrew