Do not set this to overwrite SPV3.2, just simply delete or rename it. If any of these are true, then you will be prompted to install the game to your documents folder. SPV3 will look to see if you have a legal copy of Halo PC, Halo Custom Edition, or if you have Halo CE Anniversary installed via steam in it's default location.
Simply download the zip file, run spv3.exe and hit install. The install process for this can't be easier. Down below you’ll find the basic instruction:
Installation is fairly simple but we suggest reading the instructions nonetheless. In addition, it packs new graphics features like ray-traced SSR and a new MCC validation system. New additions include the new Firefight mode – the single or cooperative campaign mode also included with Halo 3: ODST and Halo: Reach, new skulls to modify the game’s campaign missions, additional new weapons, armor, and other customization options.