Delete or rename logo_1_akella.bik, logo_2_RWS.bik and logo_3_TMS.bik in <path-to-game>\p3\media.
Effectively an unofficial patch of sorts; fixes many of the game's issues whilst also reimplementing some of the game's missing features/beta content.
Use POSTAL III NODRM.
Allows you to play the game in first person mode. Paste the script in your autoexec.cfg.