Cannot use GetThumbnailImage

I was looking at the GDI+ wrapper and trying to figure out how to resize an image in memory (w/o drawing to a picturebox, etc). I assumed this could be done with the GetThumbnailImage of the GDIPImage class, but I was unable to successfully call the function. Do you have a sample? In .NET, it appears you can pass Nothing as the last two parameters, but doing the equivalent in VB6 (passing 0 or null) is not correct, and I wasn't sure of the callback function definition, though in .NET it appeared to be a simple function that returned a boolean, so I tried:

and...

but this too failed. Any guidance would be greatly appreciated.