extract file from backup

I backed up my laptop (Inspiron 9300) onto an external harddrive right before it completely crashed at the beginning of the month.  I used the WindowsXP backup utility to do it.  I then reloaded Windows onto my system and decided not to reload everything--as I saw it as an opportunity to have a cleaner machine.  However, there is a Very Important file on the back up that I need to extract it is in the "Total system" file of the backup.  Is it possible to extract just that one file, or do I have to open that file?  And if I do open that file, will that reload Everything that was on my computer before it crashed?  I hope I'm making sense here.  Thank you to anyone who can offer some help!

-Lisa