Some answers here:

1. Pressing spacebar will lead DirectRT to the next trial.
2. Video quality is generally the same in DirectRT and MediaLab--both use the Windows MediaPlayer video engine.
3. Video are usually pretty easy to load into MediaLab--check out the section in the users guide on the Movie item type and also "BackVideos".
4. You can embed a DirectRT session within a MediaLab session by use of the DirectRT item type.
5. Data for DirectRT sessions should be located within a "data" folder located in the same place as your input (.csv) file.