All actions (as long as you didnt change the path when installing cs3) are stored in <hard-drive>:/program files/adobe/adobe photoshop cs3/presets/actions
Just copy them all from there to somewhere else, maybe My Documents/photoshop actions
Remove and re-install CS3, then copy them back to the above directory. If CS3 is running when you do the copy back, you will need to restart cs3 to make them available.