I know a lot of people swear by paint.net but I think you should try out
inkscape, it's probably a better tool for what you're trying to do. Here's a windows logo I made in inkscape:
http://dl.dropbox.com/u/11513588/vista%20logo.svgFirefox, chrome, safari, etc will probably display it as an image. Internet explorer still doesn't have svg support, although it's been partially implemented in IE9 so you'll see nothing or get some kind of error. Just save it to your desktop and open it in inkscape. Try clicking stuff and dragging it around and note the difference between a vector editor and a raster editor like paint.net. If you're interested in learning more, inkscape has a really good basic tutorial
here.