Most likley this is due to one of the following things: Autoscaling or a non-distributed font. The DPI resolution will always mess with you as Charles pointed out. But in this case, it could be the Autoscaling on the form:
This has bitten me before as well. You can adjust this to prevent auto-scaling altogether. The second issue may be if you are developing with a font that you are not distrubuting. In these cases, the default system font will be used which can cause these types of issues. For example, we use Calibri and Segoe UI in our medical application a lot. However, these are distributed only with Vista machines which means that we had to take this into account on our installation.
Hope this helps.