ive seen MANY people use FL studio, but unless you use a Torrent, you have to pay $100.00 or something to buy the Full version... (a torrent is basically like illegally downloading it, alot of people do it.. i cant tell you how, because i don't know how xD haha my friend does though...) [Oh and btw, you have a nice profile picture :D]
To create a dubstep remix, you will need to get a software program like trakAxPC Pro. This software will enable you to remix after editing a combination of video, audio and even photos. It also allows you to export the finished final remix as MP3.
Depending on what PC you have, I made a dub step song on my macbook with garageband, all you have to do is select percussion tools, mixer, tune and then just play, then you will have created the beat which is the backbone of a dub step song, then you add music, other software for microsoft include things such a : windows music mixer, microsoft music maker and instrument tool pro, I don't know about that last one though, never used it!