I think Inkscape is a vector-based drawing app (didn't look it up now) like CorelDraw right? This means that you have to export your drawings to raster graphics images (=bitmaps) first, before you can use them in DarkGDK. I don't know this app really, but you should be able to export to BMP, PNG, etc.
But that's just the technical part, the other is the art itself. You have to be good at that to achieve graphics with a decent quality you know
I think if that's the kind of info you desire, this thread would fit better on the 2D board rather than DarkGDK...
Now the plot thickens, the fps decreases, and the awesomeness goes through the roof.