If you are not storing state secrets on the drive, I doubt anyone will go through the trouble of hacking your drive to get to the data even if it's easy to break the security. There are tons of programs that can encrypt individual files, TrueCrypt is a good open source one. Full disk encryption is more secure as every file is encrypted. If you encrypt only the MBR and file tables, the files are open, and someone can just clear out the file table, and use a file recovery program to re-created it. If every file is encrypted, any data on the drive will look corrupted unless they have the encryption key.
But, unless your name is Bill Gates or Walton, anyone that steals your PC is trying to sell it to buy crack, not steal your yahoo password. You should be more worried about keeping backups of the data than encryption. So use your light encryption method, will be fine.
That encryption is not powerful at all. Every day, we answer posts from people who seem to have partition table corruption. They go and use some sort of sector-by-sector clone tool and usually recover their files.
Anyone with a copy of Clonezilla can defeat that encryption. Try it, if you have the time.