how do i reinstall the systems preferences app

Download Combo updater. http://support.apple.com/kb/DL1399. It doesn't matter if you already have it ... it will refresh you system apps.

It won't refresh anything which hasn't been changed since the original release, as may well be the case. The OP could certainly try this, but if it doesn't solve the problem it will be necesssary to install from the original disks and then use the updater to bring it up to date.

If your having problems with System Preferences, it might be it's Preference file, which reinstalling the System Preference program will make no difference.

First locate the com.apple.systempreferences.plist file in your "Username"/Library/Preferences folder and drag it to the Trash.

Reboot and startup System Preferences, see if it works and if it does, reset your preferences.

If System Preferences still doesn't work, the do #8 Reinstall Only OS X, which will replace the program, then Software Update fully to get current.

Step by Step to fix your Mac

(note: if you not on 10.6, then follow the link above to find the method for deleting the file in 10.7+)