DirectRT may be a better alternative for time-precision critical experiments; however MediaLab has the capability to complete what you need.
1. The easiest way to hide a scale response is to add an extra ( l or t ) paramater. If you specify l2000, the scale responses will be drawn 2000 points to the left of their default position - if the monitor can't span this wide, the items will be drawn off screen. Does this make sense?
See the following for more information on this parameter:
http://www.empirisoft.com/medialab/h...eters.htm#left
2. This is another feature in which DirectRT excels; however psudeo solutions are available for MediaLab. The easiest way I can think of to accomplish what you need done would be to launch an EXE using the .EXE item type. The executeable being launched would need to intercept any keys that you don't want used, and keep them from ever being intercepted by MediaLab. By doing something like this, you would also be able to redirect other keys to actually send the software a numerical key. For instance, if you pressed A or L, you could use a program to redirect these keys to 1 or 2, etc.
If programming is not your forte, you could look into a program such as
http://www.autohotkey.com/ to help accomplish this task.
I hope this helps!