It depends on what you mean with "protection":
If you want to lend your disks to your friends but you don't want them to copy your data, then you're out of luck. All DVD protections are commercial and have been defeated. The only effective copyprotection system is StarForce (which is also suitable for CD-R and DVD-R) but I've heard somewhere it was defeated recently.
If you want to lend your disks to your friends but don't want them to access your data without your permission, then you can password protect your files -or- use some good encryption programs like Encryption Plus which make data unaccessible unless the user knows the password or has a special keyfile.