If I get a new motherboard???

yes you may need to re-install windows due to the new motherboard using different drivers--you may or may not get away with just plugging in the old hard drive but i wouldnt rely on it

if you are using windows 7 it has built in backup

go to start and type backup in the search box and select backup and restore from the list
Maybe you will need to reinstall Windows. Maybe not. My experience over the last 10 years has been that using and old Win install with new motherboard works about half the time. Your odds are better if you stick with the same brand and chipset family (like Gigabyte P35 to G'byte P45). Your odds are much lower if you are changing between Intel and AMD processors.

Backup your data, plan for the worst, and hope for the bset.
So, if i switch from a p67 board over to a z68 board, I will most likely have to back up and reinstall windows? Can I back up my files to an external, and over write all of the newly installed files? Someone please teach me how to not lose all my files after the new install :p