i was actually lookin around for help on the same topic and came accross this.
the reason this is happening i think, is because you have one soundcard doing the input and output so when you record a separate track and still want to play the track you just recorded, its picking up and playing it out of the same soundcard and recording it onto the new track as well.
this was not a problem for me before, because i had 2 soundcards and had the soundblaster one as the output, and the echo darla as the input.
that is the only way i found to do multi track recording and not run into this problem...but to me, that is super dumb and there has to be a way. i dont think it is mandatory for you to have 2 soundcards to do multitrack recording and not run into this problem. i bought the newest soundblaster audigy 2 card and it has an ice 1/4" input on the front of it..plugged my guitar in, recorded, crossed my fingers and went to do a second track and its picking up the first track.
its making me crazy, and i just sold my echo card on ebay thinking it would be of no use to me.
someone please help...i tried my recording properties in control panel and it didnt help me out at all.