CharleyO's advice is sound. There are good malware cleanup guides around the net, MajorGeeks has a good one
http://forums.majorgeeks.com/showthread.php?t=139313 Probably no need to go through the entire procedure, unless the indications are that something is not right.
I'm assuming (mainly from your old, earlier posts) that you use XP home with SP2. A more streamlined way to proceed, rather than downloading incremental updates might be to download the installer file for SP3.
http://www.microsoft.com/downloads/details.aspx?FamilyId=5B33B5A8-5E76-401F-BE08-1E1555D4F3D4&displaylang=en it says here that this file (a whopping 316.4Mb) is intended for it professionals to update multiple computers on a network. It didn't prevent me from downloading it myself, though, simply because I wanted to save the installer in case of Bad Times.
The other, and recommended, way to do it is visit MS Update, and select only SP3. Let it do its thing, then revisit MS Update to see what further is required. You will see that the list of updates has shrunk considerably.
[edit] correct file size.
If that helps, and you are interested, I have some ideas for behavioural/settings/application thingies you may wish to put in place afterward, to semi-automatically take care of being up to date.