I don't know if there's anything special about this Belkin media reader, but if it works like any other card reader, then the card will mount on your desktop like any other drive or disc, and you can put whatever files you want on it. I use my SD card with my Palm Tungsten and digital camera, so at any time it could have MP3 files, pictures from the camera, applications and files from the Palm, or a mixture of all of these sitting happily together in folders like any other drive. My card reader is a PC Line SD/MMC card reader from Dixons, it cost £15.
Edit: Umm, I just realised, this Belkin Media Reader is the iPod add on isn't it? Well according to
this PDF file spec sheet, it's just for images and from your camera and snuffing around ipoding.com, it also does quicktime movies.