My mega mod which is currently on the back burner uses textures that are 4000x4000 for everything which gives highly realistic looking textures.but with the extreme downside of needing a very powerful setup to avoid major in-game lag.
Think of resolutions of 320x240 and so on.those are about the size of the textures for the ps2 version.where the pc version uses textures that are anywhere from 512x512 to 1024x1024 in size. There is a lot of bump mapping and displacement mapping involved in order to fake things like extra details and such while keeping the textures at a extremely low resolution. I really wouldnt even both attempting this since the ps2 textures are extremely low resolution and they only appear to be higher quality to the pc version due to a little bit of trickery with the textures.