Here is a quickly thrown together list of ideas you can try and discard as you wish.
Try System Restore to a point before the skipping appeared.
Skipping Sound
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811982 - How to troubleshoot playback in Windows Media Player 9
Troubleshooting DVD playback
Resources for Troubleshooting DVD Problems in Windows XP (Q308012)
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Q: Why does WMP play too fast or too slow?
Read the answer here.
Have you checked the following.
Control Panel/ Sounds and Audio Devices/ Audio tab/
Make sure you have the correct device listed in Sound Playback.
Run the DxDiag from the Start Run box, see if that picks up anything.
Use MsInfo32 the same way too.
Have a look in the Event Viewer for any errors. Look in the System or Application folder. You can
get to the Event Viewer via right click My Computer icon and select Manage.
Any errors logged in the Event Viewer can be expanded by double clicking on the error line.