the first few files I madeI used xstep, then I just switched to using notepad.
you don't just convert an mp3 to a stepmania usable file.
you have to make a dwi or .sm file to do it, I like .dwi. There are tutorials out there that can tell you how to do it a whole lot better than I can but xstep was nice what the file should actually look like when it's done.
basically, unless you get some sort of satisfaction out of it, it pretty much isn't worth doing.