I hope you plan to do the initial sync locally
There is no official Apple provided approach to do this, but there are various ideas you could consider. Firstly you are going to need to organise some means for the two servers to be able to communicate with each other over the Internet. A site-to-site hardware based VPN providing a permenant connection would be the easiest and most reliable.
Secondly, you will need to use some software on each server. A common tool for syncing two computer volumes is Rsync see http://developer.apple.com/library/mac/#documentation/Darwin/Reference/ManPages/ man1/rsync.1.html
Many Mac backup utilities have a similar capability to backup to a remote host. Some use their own protocol for doing this e.g. Retrospect, some use standard FTP, some rely on you first logging in to the remote file server so it is available on your desktop.
Another different approach you could consider would be to use a pair of NetGear ReadyNAS boxes. These are self-contained 'servers' although not ideal for use for Mac OS X network home directories. NetGear provide an add-on service to synchronise two (or more) ReadyNAS boxes. See http://www.netgear.co.uk/business/products/software/readyNAS-replicate/default.a spx this also does all the hardwork of letting both ReadyNAS boxes find each other without having to setup a VPN system.
Thank you very much for the response. The rsync approach looks very interesting. I would really like to stay with Apple hradware/software as the support is outstanding and it supports all of my macs fully.
I think I am going to need to find someone to help me set this up and make it work as I don't think I have the chops to do it myself.
Again thank you very much for the information.
Just to add my two cents, the rSync way is very effective if you set up a rsync instance on both servers, as they communicate and just send the modified files parts.
the rsync man page is very well written, just needs a bit of time to check all the options.
You can schedule the rsync with a .plist file on /Library/LaunchDaemons
If you don't know how to do that there's a precious piece of software called "lingon" you can find in appStore. It will help very clearly to do that.