Zelda, it is possible for multiple installations of Trainz to run side by side. Simply install Trainz a second time, only now you direct it to a second folder (example E:\TS12B). Important note, when you run the patcher and it asks where Trainz is installed, direct it to the TS12B folder. This way, if you find that SP1 is not for you, simple run the uninstaller in TS12B folder without affecting your main TS12.