Okeydokey
Models:Either DarkMatter or gameSpace or trueSpace3.2 or gmax
Music:Finale Notepad. Use your PC mic to record wavs, or pay $20 to
get MIDI export
Sound FX:Your oral cavity and a PC mic, or SoundMatter.
Textures:MS Paint!!! It is still good. Or if you can bounce it
Paint Shop Pro.
OutdoorLevels:Magic World from all-seeing-i.com
IndoorLevels:Just use a modeller, or 3d Map Editor, or even better- Cartography Shop.
Collisions/Gravity:Nuclear Glory's DLLS
Actual Development: DBP or DBC, if you get DBC get Enhancement pack
These progs are your friend. Pay special attention to Magic World, edit matrices, make them bigger then allowed in DB, make multiple matrices, put 3d objects on them, then load them using a function provided royalty-free with the software. Plus the whole thing itself is free. Uses analog matrix height adjustment instead of tile by tile editing.
My fingers are tired.........
Juvenile Industries
Current Project: The First Room (FPS)
Soon to come:An rts, and a snowball fight game