Setting the interval to zero means your game will run at the maximum speed. This isn't always the best thing, however, because it will also mean that your game will run at different speeds on different machines (as you discovered yourself).

To counter this you could try a different setting, say for example 16, (~60fps) which will give similar speeds on different pc's.... most of the time anyway.
In case of 2d games, 60fps usually is more than enough.

However, if you want speed to be the same on all pc´s no matter it´s configuration, you really should get yourself familiar with delta time, or timebased movement. There are several threads about it here on PGD, including code samples. In short it means that your sprites don´t move with a certain pixels per frame, but rather with a certain pixels per timeunit.