Just to let you know, I'm probably gonna use them in the GIMP. I just need to figure out how to add them. (I know how to do it, but I don't have the GIMP folder with all the stuff in it because I didn't install it. It came automatically with Ubuntu: Linux. >.< )
Well, in my opinion, the term vector brush is probably incorrect in the way it gets used, particularly in GIMP. Vector images and bitmap images are common computer applications. Rather than try to explain it myself, here's a link that does a pretty good job of it....[link] Or, you can do a Google and find more explanations.
Vector brushes, for the most part, are made up of simple lines, curves, circles, and other common basic geometric shapes. They don't rely on a lot of texturing to make them look real, but are meant to be simplistic. (Mind you, this is my definition)
The nice thing about real vectors is that they can be scaled up or down to ANY size without any loss in quality. Try that with a bitmap (aka raster image). However, GIMP doesn't have true vector capabilities. So, even though the brushes are called vector brushes, that term only applies to the fact that they are made of the simple shapes. The brushes themselves are actually stored as bitmaps (rasters) and will lose quality if scaled up in size too much.
There's a "Download" link on the left side of the screen near the preview image. Click it, save them to a convenient location (like your desktop), and extract them to the GIMP brush folder. Refresh your brushes in GIMP or restart GIMP and you're ready to go!