If you are having problems with speed-related bugs in Quest for Glory I to IV, may I pass on the suggestion that you try running them using DosBox (a number of the QFG fan sites suggest it)
available here by clicking the Programs link, listed under Utilities, in the menu on the left
or Main Site:
http://dosbox.sourceforge.net
I found it pretty good, and have loaded a QFG4 save from just before the Swamp and finished it (due to some quirk or other, on the final screen, I had to put Speed slider to max., Detail slider to min. to finish it, but that is a known bug).