If you have a mass of folders with more media within them (as is with most stepmania folders), in Windows XP it loads the metadata from any video / sound file, while getting thumbnails for any images. Even if you have it turned off. I ran into the same issue when I found Windows Explorer taking forever (and even crashing) when trying to navigate through my manga or mp3 folders.
It's possible to turn these off, but turning off the image preview thing will also remove Windows Image Preview viewer, so I started to your Infranvew (or whatever it's called).
If you feel kinda risky, you can try this:
the jackol’s den » Windows Explorer Freeze problem - Mikhail Esteves