My font in the system has been changed ?

i have macbook 10.5

my problem is :

The font in the system has been changed .

can some body tell me how i can change the font to normal .My font in the system has been changed ?
may be you have been attacked by some viruses or deleted some system files. If it has happened in the recent time use system restore to a date when your system was perfect. if you don't know the process how to use system restore the visit the below link



http://advancetechnology.today.com/2008/My font in the system has been changed ?
Open the Apple menu and choose Control Panels, then Appearance.

Click on the Themes tab to change the look of title bars, windows and progress bars.

Click on the Appearance tab to change the overall look of menus, icons, windows and controls; to change the highlight color for selected text; and to change the variation color for menus and controls.

Click on the Fonts tab to change the large system font (menu bar and headings), the small system font (explanatory text and labels), and the views font (lists and icons