All you need is Paint. You can capture an active windows or whole desktop.
- if you want to capture only the active in Windows press alt+PrtScrn and if you want to capture all screen press just PrtScrn (Print Screen) - open Paint and clic edit->paste, or press CTRL+V (to open Paint go to START->All Programs-> Accessories-> Paint) - finally, save your snapshot in .jpg, or .bmp
