I'm working with the HC(S)12 right now, but hopefully some of what I know will apply to your situation.
1) If the 9S08GT60A is a HC08 derivative, what tools you have should still work. You may need to do a minor upgrade to include that deriviative's header files if it's new.
2) Check with licensing@freescale.com.
3) If your current version of Codewarrior supports the 9S08GT60A, then just open the old project with Codewarrior. However, to ensure that you get the proper default settings for the new processor, I'd opt for using Codewarrior's New Project Wizard to build a 9S08GT60A project from scratch, then add your source code to that.
---Tom