window minimize/maximize slow after using Windows Media Player 11

After I watch a video (.wmv file) in Windows Media Player 11 on my Thinkpad
R40 running Windows XP Pro SP3 and close the Windows Media Player 11 window,
it causes problems maximizing and minimizing other windows (the windows
maximize or minimize in slow, jerky movements). It's very annoying and the
only thing that I've found that gets rid of the problem is restarting my
Windows XP which is very time consuming. Does anybody know what is causing
this and how to fix it? I need to be able to watch training videos without
having to reboot my computer after watching every video. My Thinkpad R40
has 2Gb of memory and 16kb of graphics controller memory.

Thanks in advance!