For those as sketchy on filesystem types as I am, it seems to be pretty basic. In the README on the original ext3 download page, the author answers the journaling question:
Q: What is journaling?
A: It means you don't have to fsck after a crash. Basically.
This is useful, because it means that every time your screen whites
out and crashes while choosing the right video card
(Section 1.2.1), you don't have to sit through an entire
filesystem check of every inode. The filesystem still fscks
itself every X mounts or Y days, but doesn't put you through the
entire wait every time you crash it.
To convert partition,s to the ext3 filesystem, you need to cleanly
unmount them, boot something else (like the Debian CD you installed
from -- see Section 6.2 on how to do this), and then, on a
tune2fs -j /dev/hdaX
wherein /dev/hdaX is the partition you want to add journaling to (hence the `-j' flag).
Don't forget to modify the lines in your /etc/fstab to reflect that the partitions in question are to be mounted as ext3, not ext2. When cleanly unmounted, they can still be mounted as ext2, but the whole point of changing them was so they wouldn't be.
That's it. When you reboot, your partitions should come up as ext3.