Windows Media Player is displaying as square pixels, making it a 20:11 aspect.
720x480 is 3:2 aspect when squared, which is also wrong for display.
Both should be using non-square pixels in 4:3 aspect.
WMP is honestly a really, really, really crappy video player. It always has been, all the back into the 1990s. It's good for audio, but that's about it. And even then, you can argue apps like WinAmp make for a much better musical experience.
Use VLC Player.
It's freeware: http://www.videolan.org/vlc/
You can change aspect to 4:3 or whatever it needs to be, in VLC. Just right-click while playing a video, and you'll see it in the video options submenu.