1. You can use BeSweet to convert a 6-channel AC3 file into a 2-channel surround encoded file; it's probably possible to use a multichannel WAV instead of AC3 as the source if you wish. You can choose between the "surround" or "surround 2" downmix mode; the latter supposedly being more compatible with DPL II decoders. In realtime, AC3Filter can do the same thing.
(Both these programs are free; the downmix algorithm is not officially Dolby licensed but works just fine.)

2. Yes, popular software DVD players (PowerDVD, WinDVD) include a software DPL II decoder (although it's normally only the "deluxe" or "platinum" versions of such players). If you actually want to process a 2-channel file to get 5/6 separate channels, there are several guides over at the doom9 forums.