Okay, pop in disc 1.
Next, get hpitools.zip from
Http://www.files.tauniverse.com/fu/files/totalannihilation/moddingutilities.aspx

extract anywhere.
open hpiview.exe
go to files tab>open
look in ta cd
should have a "totala3.hpi"
open it
extract to ta directory
it contiains all the ta files needed for install!
so you force install ta.
bye. :)