You can start this quest mod as soon as you start Fallout NV, basicly. Fallout New Vegas Mods Join The NCR Movies Preview Fallout: New Vegas > Videos > Bear Force One's Videos This item has been removed from the community because it violates Steam Community & Content Guidelines.
Or you earn the respect of the NCR and find alternative way to join, the choice is yours. After all, you can get President Eden to do it in Fallout 3. Others embrace the NCR seeing it as the only way out of the post apocalyptic world. 2.0 Old The locations where you will be able to join the Enclave are the Goodsprings Cemetery, the road between Novac and New Vegas and the road between Jacobstown and New Vegas.
The NCR mod allows you to join the NCR, do missions for them, rise up the ranks and join various NCR Units, unlocking equipment each unit needs as well as various unique perks. Stamping down an NCR boot on everything and claiming it as their own in the process.