For the invisible model,
First make sure the model is correctly exported. Open the w3d viewer and open your w3d file there. After loading expand the hierarchy at the left side. There should now be 1 hierarchy listed. When selecting this hierarchy you model should show up (don't worry about missing textures if there are any).
If the above is all correct, make sure you put the model in the correct folder:
{Zero Hour install directory}\Art\W3D\
If that's also correct, make sure the ini file reads the correct model name. I'm not sure but it could be that the name is also case sensitive.
For string editing:
The strings you see in game are located in a file called generals.csf. This file is located in English.big (or whatever language your game is in). For editing you need an csf editor like the found
here (third last downloadable file). I don't know if there are other/better editors but this one works well enough for me.
The texts themselves are located at three different locations. For the following part I assume you replaced the king raptor object (AirF_AmericaJetRaptor) with your own model.
Object Display Name:
This is the text displayed when you hover with your mouse over the ingame unit for several seconds. When you look at the design parameters of the object code of the king raptor you'll find a parameter called 'DisplayName' with the value 'OBJECT:KingRaptor'.
Open the generals.csf file with the editor and in the left panel find the key with this exact name. At the right side there is an textarea labeled 'value'. This is the value displayed ingame at every location where the ini files make a reference to this key. Change the value to the value you want.
Commandbar Text Label:
This is the text displayed when you hover with the mouse over the button in the controlbar to build the unit. It also determines the hotkey on the keyboard that will build this unit. To find the key used for this one open CommandButton.ini and find the button responsible for building the king raptor ('AirF_Command_ConstructAmericaJetRaptor').
The key we are looking for would be 'TextLabel' which has a value of 'CONTROLBAR:ConstructAmericaJetKingRaptor'. When you look up this key in the csf editor you will notice that in the value there is an '&'. The character followed directly after the '&' is the hotkey you can use to build the unit. Change the value to your liking.
Commandbar Tooltip:
I don't think this one needs explanaition but as I've done it for everything so far, it is the text saying what units it is strong and weak against. Like the Text Label it is also located in CommandButton.ini and is called 'DescriptLabel'. The key for the king raptor would be 'CONTROLBAR:ToolTipUSABuildKingRaptor'. Like the other texts, change as you like.
The build cost is automaticly added by reading the BuildCost of the AirF_AmericaJetRaptor Object.
Save the csf file and place in the following folder:
{Zero Hour install directory}\Data\English\
Notes:
When closing the w3d viewer it wil report an error, don't worry about that, it's a feature.
When editing the csf file, don't use the delete key to delete text in the textarea as it will remove the entire key. Use backspace instead.
Edit:
Hmm zogle beat me to it... well now you two explanaitions and he also included the images that I forgot...