Exellent for a first try!
Keep up the beat! You did very well for one of your first attempts.
I recommend you to try and brows to: http://8bc.org as it has many great aspiring tunes for you to learn from as well as http://pown.it that has some outstanding examples of what you can do with your music as well as directions you may like to go trough.
I myself is an artist here and you can check some of my better works here as 8Bit mixes that I made to themes from Mario 64 and Mario RPG.
If of course have many moudles in this website that may benifit artist to use and create, and it would be lost if both of us as well as other artist wouldn't be here.
more of my examples can be find at my web site: "The Nastorama"