Ghost image on monitor

Using: Windows XP Home -- SP2 downloaded but not yet installed
Computer: Compaq Presario 1.4 MHz
Memory: 256 mb
Video: Intel 82815 Graphics Controller
Monitor: Samtron 76DF

When I close a window, a portion of the image from that window remains on
the screen. It is always in the same location, in a band about 1 inch high by
6 inches wide. Eventually, as I begin to work in a new window, the "ghost"
image clears. This has just started to occur on a Samtron 76Df monitor that
is a little over 2 years old, purchased with the Compaq CPU.

Last new software installed was SBC Yahoo DSL and a Linksys wireless router,
about 6 weeks ago. Everthing worked fine until the last day or two. Should I
be looking at a problem with the monitor or the video controller? Is there
any disagnostic I can run to better isolate the problem?

Thanks, pekey