Try using Paint.NET. You can get it for free here. Simple open your DDS (by default, DDS is supported), grab the magic wand, select your white area (or where you want to be transparent), and hit "delete". The selected area will instantly become alpha channeled. This probably is not the best way to do it, but it works. If you want it professionally done, attach your DDS and I'll see what I can do.
Also remember that PNGs do work as well; they're almost just as good as a DDS, minus their size (slightly larger) and single layers.
Also remember that PNGs do work as well; they're almost just as good as a DDS, minus their size (slightly larger) and single layers.