LR 3 file mgmt / backup
The changes are kept in the LR database/ catalog - in my PC Vista computer it is in
You should always back this folder up in an external drive as well as your photos.
If you lose everything on your D drive you can load your photos back onto D: and LR will still apply your changes. If the folder structure is slightly different, or the new drive has a different letter you can right-click on the folder in LR and then 'Find Missing Folder' and LR will still have your settings.
You don't have to worry, you are totally covered at the moment, but I would always backup the catalog ( the .lrcat file.)