Ok...update here I did get some kind of VC installed but messed up. I think its down to the textures. The turatorial says to put the texture confg file into every texture of the plane. When I do this it ask to over write the file,is this ok.Also do I use the entire F-18 texture folder or just parts of it.
You need to understand how FSX manages textures and then apply that knowledge to your situation. The reason it's asking you if you want to overwrite a file is because it's found an existing file with the same name which is to be expected if the original aircraft was set up correctly according to the FSX SDK. The tutorial you are referring to is showing an example for using FS9 textures in FSX which is slightly different to your case where I believe you are trying to add a different VC to a true FSX model.
Let's deal with the 'texture' folder first. In FSX this folder contains
all the textures used by both the external and internal models (the exception being any textures for the pop-up panels/gauges which are kept in the 'panel' folder).
Now let's look at the repaint or secondary texture folders. To save disc space FSX only needs to have the specific textures required for that variant in the 'texture.abc' to 'texture.xyz' folder(s). In each of those folders there will be a 'texture.cfg' file which tells FSX to look in specific folders to find the 'missing' textures which are
common to all variants. FSX will look in the specified directory as defined in the aircraft.cfg file first and then will look in the folders defined in the texture.cfg file if it is missing textures.
In your case you are trying to add the default FA-18 VC to a model of the T-38. The reason you are not seeing the correct textures is probably because you have either not copied the correct files over or you have put them in the wrong place and FSX doesn't know where to look for them.
The first thing you need to find out is if the T-38 has a default 'texture' folder. If it does than you need to copy the VC textures from the FA-18 'texture' folder to the T-38 'texture' folder. Someone familiar with texturing/repainting/model making would be able to identify just which those files are but if you are unsure the only option you have is to copy the entire contents of the FA-18 'texture' folder into the T-38 'texture' folder (the non-required files will be ignored). Once you have done that then the FA-18 VC should appear correctly textured as the files it requires will be in the correct location.
If the T-38 does not have a default 'texture' folder then the problem becomes a little more complicated.