I had have the same problem, but I solved this witn Image Edit that come with VFP5, the trick is:
Create a ICON with two Icons One of 16*16 and other of 32*32, Explorer shows the 16*16 icon if You choose Large Icons then Explorer shows
the 32*32 icon, the only one thing than I have'nt do is 256 colors or more for Icons due I use ImageEdit than only works with 16 colors icons.
I will try to adquire a more sophisticated Icon Editor

I hope this help.