Actually, that Tileset Maker isn't really the "standard" way of people importing tilesets.
The standard way is to use your favorite paint program (MSPaint, Paint Shop Pro 4, Photoshop, GraphicsGale, whatever). Each tile is 16x16 block in that image, and death magenta (RGB(255,0,255)) is used for transparency (Verge has no notion of alpha channels -- yet, anyway).
Then save to a flat image like a png or bmp. The use the Import dialog in Maped itself, and select some sort of image source and import!
I actually cover the steps to this in
one of my tutorials, and
in the Maped documentation I helped write.
This should give you the .vsp tilesets you want!
And for .chr files, you can USE VOpenCHR, but you could also use the CHRMAK tool. CHRMAK is commandline, but it's slightly more handy if you want to turn image files into .chr and still freely edit with whatever paint program you want.