It comes with its own MP3 player, but you certainly aren't tied to that player. The MP3 files are fully transportable. You can connect PopCatcher to a personal computer via its USB cable and use iTunes to load your new music library onto your iPod.
If I'm reading the webpage correctly, PopCatcher costs about 1500 krona which equates to about US $200. It seems to be for sale exclusively in Scandinavia at this time although they're taking notification requests for other countries.