How can I sync photos and videos from iPhoto to my windows server
You can move the iPhoto archive in your Photos folder in your Home folder to a location on the external drive, create an alias in Mac OS X from the new location, and drop that where the archive used to be in your Photos folder in your Home folder. iPhoto will automatically redirect to the external drive. I do this at home and it works great. As long as that external drive is backed up, you're all set. 

Otherwise, you will have to use backup software (not Time Machine in this case) to ensure backups are made from the internal HD to the external hard drive on an automatic, ongoing basis.