Press the Prt Scr key on your keyboard.
The snapshot is saved in memory so you then press paste in an imaging programs such as Paint, Paintshop, Photoshop etc.
you can also press alt+Prt Scr.
This will only take a snapshot of the active window
Windows XP Pro 2002 (SP2)
Intel Northwood 2.4GHz
Compaq Evo D510 SFF
768MB DDR PC2100
NVIDIA TNT2 32MB
Intel 82801 (AC\'97)
C: 40GB (FAT32)