Hey blue_thud, OK so you have the zip or rar file for dynamic sounds pack, make sure it's for your current version of OFP or it might cause you problems..!
Open the file in winzip or something similar... Without this it's a non-starter... You should see one folder inside called DYNAMICRANGE (if I remember correctly)... Open another window on your desktop and browse to your OFP directory, so you can see the OFP exe files etc... Then go back to the winzip window and just click and drag the DYNAMICRANGE folder into the OFP folder... You should see two sub-dirs in the DYNAMICRANGE folder BIN and CONFIG (I think), with one file in each one .pbo and one .cpp... Just add the -mod=... line to your shortcut, no quotes or anything and give it a go...
That should be it... Hope this helps...