We are wanting to backup our quick books files in multi user mode to an external hard drive, is this possible?
Sure. In the evening when noone is using it.
Pretty much that is it, or? At least it was last time I checked. It is file based, keeps locks around, you are likely to not get a consistent database image. If you have nigher uptime / people requirements, you need to move up financially to a system using a database server or some sort.