Nicely done.
The track is well put together, and your drumwork is solid. Though it all sounds very synthetic- I suggest putting a few effects over your drums at the least.
Otherwise the only other problem I had was that you encoded this to 320kb/s! For the audio portal this is just blatant quality overkill. 128kb/s stereo is good enough for any song that will be listened to over the net (or downloaded).
You will find that you will be able to fit ALOT more into the 4MB limit this way, also.