Those are totally valid questions. I guess hard depends on a person's experience with sequencing music in MIDI. I've been sequencing game music for about a year now and I find the hardest part is simply listening by ear to the original song, in this case a real audio file of the arcade song (from the arcade home page), and working to the best of my ability to recreate each and every note contained within, but in stereo and on separate tracks.
This means I normally start by listening to just one single measure of the song repeatedly, over and over again, going into the staff and placing a note correctly, going back to the song to listen again, placing another note on the staff, repeat, repeat, repeat until the song is finished. You have to be patient, persistent and somewhat mentally stable to spend hours to create a one minute piece.
The result is that I take great pride in offering you and myself a piece of music history that is midi-immortalized (if that's a term).
I'm glad you enjoy the tunes. The program I use btw is called Sonar XL 2.0, a MIDI sequencer and general music multi-track recorder software program by Cakewalk.
If you open up the songs in any MIDI sequencer (you can probably find a free one on the web somewhere if you search) you can view the sheet music (staff rolls) for each individual track that I created, which is a great feature only available in MIDI sequencers.
Feel free to catch me on AIM as well if you have any other Q's.