you need to install patch first(1.0.7.0: better graphics, useful for modding 1.0.4.0: normal graphics, better modding performance(what people say, but i use 1.0.7.0 and work properly too)
then install razor crack(comes with the patch, i think)
also add this files to the main folder:
dsound.dll (asi loader)
scripthook.dll and scripthook.net.dll (depends on the patch version.1.0.7.0 uses 0.5.1 vrs)
now you can add script mods and run them
also with the patch, you are able to modify game files and add new files(maps...)
to edit models, textures, collisions use spark iv(textures) openiv(textures, models importing in open format)+GIMSIV plugin for 3Dsmax(version 2010 or higher(2012 better))
i hope this info was helpful
aacclapd.