mIRC uses MCI commands to play files, saying that... if a mp3 is playable in windows media player, it should be playable via mIRC.
and its possible your mp3s are skipping because of your low end sound card, a mp3 is 3 consecutively played compressed wave files(well not exactly that, but close to it) so it can do a number on an old piece of hardware. but anything made within the past several years(like 5 or less) should have no problem playing something like that.
