The postprocess.ini comes in the RX_CONTENT/COMMON folder. Its not as if i created the postprocess.ini lol. thats all black f's handy work and he should get the credit for it. I have just been tweaking about with the postprocess.ini settings and i have got it looking very very nice i genuinely prefer it to CM:DiRT graphics.
I dont have rbrdll so i guess u dont need it ... but u do need the rx_dll plugin. i will send u the PP.ini so u can try it out.