Try VLC PLAYER and see if it works. If so, you need DVD player software which is never included with XP Home or XP Pro.
I'm having a bit of a problem...when I try and play a DVD movie on my XP installation, the picture won't display at all: all I see is a blank screen; there's no picture. The blank screen might be a different color, and there might be a different colored square or two in the display. I can hear sound (a lot of the time anyways), but no picture. This problem does not occur in my Windows Vista installation on the same machine (and that installation has very little installed...including just the default Vista codecs). The DVD drive itself works fine; movies play perfectly in Vista, and even XP has no trouble reading DVDs (WMP11 in XP recognises the disk in the drive, games play with no problems, etc.). Even after installing FFDShow, it doesn't work. Any ideas?