There are no built in tools in Calibre to do this. You will have to use external tools för file sync. If it is easy to do, or not, is up to you. One added benefit is that you may get a good backup system for your Calibre library.
Consider the the Calibre library on your laptop to be the main library, and the Calibre Content server library on the HTPC to be a backup. And have another backup beween the two.
So you have up to three copies of your library:
1. The main Calibre Library on the laptop.
2. Backup A, written from the laptop, on the HTPC
3. Backup B, also used by the Calibre content server on the HTPC.
Then, after changes on the laptop, update Backup A on the HTPC using some sync software.
Then restart the Calibre content server and at the same time also sync from Backup A to Backup B. (Or delete Backup B and move Backup A to become Backup B.) You may also wish to keep a few more generations of backups.
In this way you can initiate a backup from the laptop at any time without first having to shut down the Calibre Content server. And after that, when needed, restart the Calibre Content server to update that library.
There are many different sync utilities available that you can use to sync between the different libraries.
One example is SyncToy from Microsoft:
http://www.microsoft.com/en-us/downl....aspx?id=15155
I do something similar to this, but I have the main Calibre database on a SSD-disk on my linux desktop and Backup A is on a linux based NAS, running rsync. I update Backup A automatically from the SSD every other hour. Nothing happens unless something is changed. My Calibre content server also runs on the desktop, but in a virtual computer using VirtualBox. When the virtual computer is started it sync a local Backup B inside the virtual computer from Backup A on the NAS. I am considering moving the content server to a small Dreamplug computer instead, but I don't actually use the content server very often.