RPGM2k3 version:
http://www.sendspace.com/file/ss1q7fEach tile have a size of 16x16 pixels.
Chipset:
The basic Chipset size is 480 x 256 pixels and must be saved either directly imported and put into PNG. format or can also be accepted as a Bitmap 256 colours style(it wont work with the 24bits colour or JPEG,JPG).
Panorama:
To be able to use a map that have 20 x 15 and have a background that will fill exacly this space, your original file (again must be Bitmap 256 colours) and must be 320 x 240 pixels(i personaly use Paint to work with and that work just easy and perfect to size up the image using the little scale tool down the software.
Charset:
Generaly 288 x 256 pixels standard (as usual Bitmap 256 colours)
Faceset:
Generaly 192 x 192 Pixels standard bitmap 256 colours
Gameover:
Generaly 320 x 240 Pixels standard bitmap 256 colours
BackDrop:
Generaly 320 x 240 Pixels standard bitmap 256 colours
BattleCharset:
Generaly 144 x 384 Pixels standard bitmap 256 colours
These are the basics but i would say that the best to avoid incompatibility is to simply edit file that already exist and build your home made stuff over those in place and then do a lot of test to make sure it look ok once in the game.
Enjoye!
Elistios