You can use Adobe Illustrator or CorelDRAW to crate SVG's, but both of them are expensive.
But with Lunacy there is a great, free alternative for Windows out there (I'm currently in the learning process). Not to forget Inkscape.
I'm not a programmer, but including an SVG renderer shouldent be that hard.
Don't get me wrong, I don't want Stardock to remove PNG support from Curtains, I just say that SVG support can be a great chance for this nice piece of software - monitor resolutions are getting bigger and bigger, pixels are getting smaller and smaller.