Question about multiple XP users and 2 TB Essential

I have a 2T Essential connected to my unit running XP SP3. I installed the WD software and did a backup. I was on my personal account when I clicked backup, I then left the machine on and went to bed. My question is there are 3 user accounts on my machine. 1 personal, and 2 others that are my businesses. Do I need to perform a backup while logged on for each account or does a back up under any account automatically back up everything but system files? When I switch to one of my business accounts I see a list of backed up data in differing categories on both columns. It differs in total MB from the total MB backed up in my personal account. However there is no Email backed up on the bizz account. I clicked the details link and email is checked on the menu as an item to be backed up. So what I need to know is do I log on to each account seperately and run a backup? 

You need to log into each account and run a backup. The backup softwares does not backup the opertaing system or the programs installed on it. Only your files will be backed up.