Introduction
This tutorial will cover how to unwrap an object to a non-square map grid (ex. 1024x512, 512x1024)
Tools Needed:
3ds Max or Maya (This tutorial is Max based)
Chuggnutts UV tools (max plugin)
Ok so take any max file you have or the one you want to do this for and apply a Unwrap UVW modifier to the model.
You will have something like this. ( I selected all of the uvs and flattened them just to make it quicker )
We don't want this square layout and we want a nice rectangular layout.
To get the rectangle layout we go to Options > Preferences from within the UVW Edit window and set the size of the wanted layout desired.
After applying the new sizes our uvs will look out of scale and this is because when we changed the height they were scaled to match the new window height.

To fix this we will use chuggs uv tools.
These are the settings I will use as we only want to shrink them by half in one direction to make them square again.
After that is applied we should have something that looks like this.
Now just layout your uvs to the new aspect ratio.

This isn't the best unwrap but it was just to show how to finish things up before sending it off to photoshop for textures.
That's it for now. Hopefully that helps you guys and gals a little bit and speeds things up in your workflow.