Movie and Video playback problems

I have a Celeron D 2.93|1GB RAM|ATI 9800PRO|80GB|100GB| computer that I use as my media center pc. I run windows XP media center edition on a new format. My problem is that every time I open a folder with MPG files inside my CPU usage spikes to 100% on the file explorer.exe. I already did the AVI file fix which didn't help. All these files are a rip from my DVR to HD and range from 1GB to 5GB. How to I fix this problem? I dont care about losing video previews or details, I just need performance.