Unison is a program to synchronize files in 2 directories. http://www.cis.upenn.edu/~bcpierce/unison/ is the homepage.
To install Unison, start up Synaptic package manager (under System -> Administration) and search for Unison. I installed the breezy version.
After unison is installed, I was not able to find a entry in the menus. Instead, I opened a terminal window (under Applications -> Accessories) and typed in unison -help and it pops up a huge list of options for ways to run unison. (You can also get help for unison by typing man unison.) I simply wanted to synchronize the music directories on two networked PCs, so I kept it simple.
On the PC where I installed unison, I created a samba share of the music drive from the remote PC (the other PC is Win2000). Then, I typed in
~$ unison /location/of/first/directory/to/sync /location/of/second/directory/to/sync
And then it started churning through the directories.
To set unison up to run on a schedule, you use crontab. For lots of info on crontab, refer to https://wiki.ubuntu.com/CronHowto in this wiki.