The basics of System is covered a little in this tutorial: http://rpgmaker.net/tutorials/1027/
About System graphics: http://rpgmakertimes.blogspot.ie/2009/05/system-graphics-part-1.html#.Vv2BVXo52UR
Making custom menus: http://rpgmaker.net/tutorials/395/
A video on making title screens: https://www.youtube.com/watch?v=00C01RpVxGk
Events:
http://rpgmaker.net/tutorials/842/
https://www.youtube.com/watch?v=EEZYriQDrH4&list=PLCV8nmYoOi4Ga8xbJvqSo4XYA4M2SC7zh&index=1 (Talk about events starts at around seven and a half minutes).
https://www.youtube.com/watch?v=p7QUWYKR0Uw&list=PLCV8nmYoOi4Ga8xbJvqSo4XYA4M2SC7zh&index=3 (about switches and variables which is related to events).
http://rpgmaker.net/tutorials/68/ (an example of commen events).
Some extra links:
Resource Masterpost: https://carmenmcs.tumblr.com/post/80839242863/go-here-for-the-latest-update-this-post-is
RMN's tutorials for 2003: http://rpgmaker.net/tutorials/engine/rt2k3/
Playlist for YNFG devs: https://www.youtube.com/playlist?list=PL05975B6152A469EB
(I couldn't find too many tutorials for RPG Maker 2003, but I hope these will be helpful. Good luck!)