XP / Vista / Windows 7 are always updating. A lot of times, those updates are Security Updates. Those keep those holes plugged in the software so you don’t have to come see us as often.
Before installing a service pack, try to grab all the latest critical updates first.
Windows XP as of 2/2/10 has Three Service Packs. These Service Packs are a large bunch of updates thrown into one pack. Before we let a Virus Removal machine go, we update their machine to SP3 (Windows XP Service Pack 3). We also run the latest critical updates from: http://windowsupdate.microsoft.com
Windows Vista as of 2/2/10 has Two Service Packs. You can find both of these service packs on our download page. You should try to install all the updates before these large ones, using Windows Update (From Your Start Menu).
Windows 7 as of 2/2/10 does not have any Service Packs out. It has been rumored one is in the making already, already beta testing on it is being done. Just do the same thing as Windows Vista and run Windows Update (From the Start Menu).
Stick with critical updates, and stay away from Optional Updates. Also for drivers from the Windows Update Screen, don’t download them “it if it aint broken”.