Windows Media Player 8 (and many other players) shrinks the video to fit it completely in the player. You can try to view the video in full screen by pressing Alt + Enter. If the size of the video is more than your current display resolution then Windows Media Player will again shrink the video.
The best option is therefore to use My Screen Recorder itself for playing videos. My Screen Recorder has been specifically designed for viewing recorded videos in actual size. Viewing options like Full Screen, Fit to Window and different view percentages, help you to correctly view screen recorded videos.
My Screen Recorder Pro allows you to generate an executable, which is very useful for distribution. The executable has a built in player, which maintains your original resolution across different PCs.