Dale,
Whenever you use one of the built-in metafonts (nidialog, nieditor, nimenu...) you can't rely on the size of this font remaining constant, in pixel terms, when you take your UI from machine to machine. The reason being that these fonts are aliases of system fonts defined by the OS, or configured by the user in a particular machine. Also, a user might chose the "large fonts" setting on a particular machine, and your "NIDialogMetaFont, size 11" will then be "promoted" to "NIDialogMetaFont, size 13" for example. If you're concerned about this issue, you should use some font other than these meta fonts. Arial 11, for example, should always be Arial 11, regardless of the user settings.
Luis
NI