Hi I just added some high resolution textures to my terrain but when i try to run the level it says "Nexus Too Small" i alter the size of the nexus but now it says "Can't create D3D texture of width 1024", what have i done? i thought 1024 was the maximum

What video card do you have? What is your nexus setting? 1024 is the recommended maximum for the greatest compatibility. It does leave out very old cards though. Did you create mipmaps for the texture?

I have a Nvidia geforce 4, nexus setting 40. I'm sure it should be able to cope with 1024, just wondering though is it possible to go higher tha 1024?

The upper limit is otherwise hard drive space. That is, if you want to use 16384x16384, do so, but no video card nowadays supports anything that high. That would require 3/4 of a gigabyte in video memory at 24-bit color. Such sizes will only be available about 2 or 3 years from now. The highest I've seen for video card support is 4096x4096. According to Wikipedia, there are several variants of the GeForce 4 series. It also seems like a fairly old video card, from early 2002. The best option is to either upgrade your video card (Radeon 9600 XT is available for $80, but I need to know your motherboard's specifications first) or create mipmaps for your texture. Textures don't use nexus, but the entities, vertices, faces, and other objects do.

You might want to increase nexus size up to 100, depending on memory requirements you're targeting.