Also of possible note to newbies, they may want to look at Ubuntu Gutsy, which can be configured to walk through full disk encryption setup during installation. Ubuntu is derived from Debian, and has become my GNU/Linux flavor of default these days, although I tend not to leave the (Free)BSD world too much.

While editing fstab it is important to put the line about swap above all, since it must be activated before mounting the rest of encrypted partitions. Remember that the order fstab gives to the boot procedure is important. The root partition must be mounted before encrypted ones. (It’s possible to encrypt root partition, too, but it’s a different thing, not this case.) If you have several encrypted partitions that use different gpg-keys, you should remember which goes first in fstab, as the boot procedure when mounting them and asking for your password will not show the partition’s name, so you assume that it is the first one it finds in fstab.
Also, it is important to put “0″, not “2″ in the last field of each line describing encrypted partitions. “2″ enables fsck when booting, but fsck does its work _before_ mounting, so you’ll get an error. Putting “0″ ensures you that fsck test will never be performed.

Fsck, when trying to check an encrypted partition says that it cannot find any file system on it and suggests to do some manual correction (that you shouldn’t do if you’d like to have your data unscrambled). If you see something like this, most probably you’ll be prompted to give the root password to edit things or to press Ctrl-D to continue. You could press Ctrl-D to follow but it has no sense, as you’ll get a mess. Enter the password and reboot, and choose single user mode when getting grub prompt. When booting again you’ll get that error once more so press Ctrl-D, and now you’ll be able to edit fstab while being in single user mode.

Good luck!