To play version 1.00 on the steam install you need a copy of RetailEXE\1.0 folder (replace C3C3game.dat with a cracked version 1.0) and a copy of CNC3_english_1.0.SkuDef from the DVD install. I think the mistake people make is either not adding the extra files in the 1.0 folder with CnC3game.dat or using a mismatched version of the cracked CnC3game.dat
https://drive.google.com/file/d/1PJXH8SaLULebXrp6LrySXpuCOVrkQ0Qz/view?usp=sharing
I have put the files in the same file structure they need to be copied into, (the 1.9 versions will be there so it will be obvious if you have put them in the correct place). Then right click on C&C3 in your steam library and click Properties, then under 'General Options' click 'Set Launch Options' and type -runver 1.0 (That's a one time thing).
