Okay Sweetie. You can download/install any update you wish to but please note that KB951072 (Aug.2008) has been superseded by KB955839 (Dec.2008). Before manually installing any update you should check the update details by reading the MS Support site for that update and checking in the installed update list in Control Panel>Add Remove Programs on your pc.
Here is the MS Support page for KB951072, note the first para labeled
Important.
I
think that as you have SP.3 installed and if Automatic Updates are enabled your system will be fully up-to-date. As you state you are "naive to computers" this would be the best way to go.
Good luck