If you're after the PS1/affine texture mapping vibe:
However you will have to also tailor your models to suit the low poly/plane look and if your serious, draw backgrounds yourself. As for downscaling the resolution itself, this is found in project settings.
Interesting side note, the PS2 was actually 1080 capable, it was just only realised in about 5 games. But I think that's why internal textures for a lot of late stage PS2 games seem to be excessive for the original 480p screen resolution. At least this would explain why games look surprisingly good when upscaled using an emulator, for example FF-12s textures at times looked comparable to Lost Odyssey's when played at 1080 on an emulator (though still abused motion blur to take the edge off the edges).