The SuperFetch service in Windows Vista preloads your system�s memory with the applications that you use most often. This makes launching of those applications much faster, but it might be an unwanted behavior for system tweakers or gamers.

Open up Services in Control Panel or by typing services.msc in Run.

Double-click on Superfetch in the list to open up the properties, and then change the drop-down to "Disabled". You can also click Stop to immediately turn it off.