Did you try running the demographics sample? Did you find that you saw only missing data in that sample??

If you need equal n's you can't really do it randomly. It gets even more complicated if you are doing the experiment across multiple computers because each machine doesn't have a convenient way of knowing what conditions the others have run. The easiest solution for equal n's is to create a subject assignment list in Excel or some other program (or numbers in a hat) that generates random values. Then use these to create an autostart file that can automatically assign your subjects to conditions based on their subject ID.

For more detail, see:

http://www.empirisoft.com/medialab/h...htm#prefs_auto

You might also look at using the omit conditions (see guide) function as a way to bypass the videos you don't want seen in each condition.

As far as centering your movie goes, it should be centered automatically if you are using a "movie" item type. If it's not centering you can manually add parameters such as (t100,l100) e.g., to have the top left corner at 100 pixels from the top and 100 pixels from the left. If the movie is a backvideo to some other item, then the parameters can be added after the filename in the filename field, e.g., mymovie.wmv (t230,l160). take a look at the section on parameters in the users guide for more details.