The differences are technical.

mstardict is based on Hildon which is based on gtk. This was the only real platform available for the Nokia 770, and the main platform for the Nokia N800, N810, and prior to a major update (pr1.1? pr1.2?) the N900 as well.

qstardict is based on qt which was written by a company called trolltech. Nokia bought out trolltech and released a version of qt for the N800, N810, and N900.On the N900 Nokia went a step further and installed qt by default when they released a major update (it was either 1.1 or 1.2, I don't remember, but I think it was 1.1). Nokia also recommended any new application be written in qt and that future operating systems may not support Hildon programs at all.

If you've ever heard of Ubuntu and Kubuntu you can sort of think of Hildon as Ubuntu while qt is Kubuntu. Ubuntu programs may (generally) be easier to convert to Hildon while Kubuntu programs generally are built using qt or at least are built using other things that are built using qt.

Meego assumes your application is written in qt while certain Symbian phones can run qt applications. Neither OS can run a hildon application.

Qt applications can be designed and run on Windows and Linux while hildon/gtk/gnome applications are generally designed and run on a Linux OS (such as Ubuntu) but with some foresight and management can run on Windows.