Hi, I´ve imported some operational amplifiers (SPICE models) to ADS but I don´t know how to create a palette to be able to use them in any project easily.
Right now, I use them copying the model and the symbol in each new project that I star
If you are copying models and symbols you must be using ADS 2009U1 or earlier so the best way is to create a Design Kit with your custom part(s). Check this for full tutorial and description of the process.
The section about "Basic Parts of an ADS Design Kit" includes a section describing how to create a component palette and also Library Browser configuration.