XP Hang Up,,avi,mpg etc,,,99% cpu

The only times it goes this way is for avi,mpg,mp3 etc(movies)..Sometimes, one click on the file, and usage goes up to 100% and my system “hangs” for 5-10 minutes with almost no hard drive activity until it finally free’s up. This “hang” problem happens frequently and randomly. I checked the processes and when my system “hangs” I notice “explorer.exe” says 99 CPU usage. And it seems like everything in the list has more MEM usage as well ..
2400: mhz
256MB RAM
XP Pro(all service packs andupdates)
ATI(latest drive)
4 Hard Drives 260Gb
Windows Media Player Series 9

: ) enjoy