To install Star Trek Online in Crossover Games, launch Crossover's "Install Software" menu, select "Star Trek Online" from the list of Supported Applications, and then click "Install" to proceed:
Crossover will download and install several components prior to beginning the install of STO, itself. Approve the installation of each component, and then approve the default install location for the Star Trek Online client and proceed through the download.
Towards the end of the process, you'll also see this "games explorer" error:
Just click "ok". Now, you'll see the final STO screen.
**Uncheck** the option to launch STO, now, and then click "finish":
Crossover's Install Software menu will then report that it's completing the installation, and will then report that it is "done". Click on the "done" button. You'll see a Start Trek Online launcher generated in a little pop-up winder window (on Mac). It'll also be in Crossover's Programs menu (on Mac) or in the Windows Applications menu section (on Linux). Click on the "Star Trek Online" icon to launch.
You will see this Internet Explorer warning when you first launch STO. Leave the check in the check box, and click "yes".
You can then login, patch, and play!
Note - during the patching process the patch client will "flicker" horribly. That's normal.
Note, also - The first time you launch STO after a patch, you'll hang on a loading screen for a long time. Depending on your system and the size of the patch, it can be upwards of 10 minutes (really). Please be patient, eventually you'll get to the game. Subsequent launches will be quicker.