Moonshell is about the only thing out there and it's fairly good. You can grab it here. There are tools to convert video in the moonshell package though I prefer to use a program called 'Batch DPG', which can be found here (thanks FAST6191 for providing a link to it in another thread).
Moonshell works fine here and is in my opinion the best option for DS multimedia.
You would do well do alter some of the options in the global.ini file, for example set dithering to 0 or 1, GOPSKip to 0, AdaptiveDelayControl=0 (you might want to experiment with this one)
You might also want to try encoding with a slightly higher bitrate and making the sounds one slightly lower.
As for controlling the movie the bottom screen has a seek bar which works well for me.