Short answer is no. You can't add pixels that aren't there. That said, be sure that whatever you are using to convert to DVD-video is doing the best job possible.
Most web video is 320x240 or there-abouts. DVD-video is 640x480. So basically you're blowing the image up 2x, which is not good. Add to that the fact that web video is always at the lowest possible bitrate, so even with adequate resolution it does not look good when blown up.