This feature was removed from our product in CrossOver 9
The Windows System tray has been with us for years. And while it's great to have quick access to some of your running programs through a tiny icon, once you've got a dozen or so of those icons running, the system tray can seriously eat into your Windows Taskbar space. Fortunately, Windows XP and Vista can dynamically resize the system tray to hide icons you're not currently using. But if you'd rather get rid of system tray altogether, here are the steps to do it (courtesy of the How-To Geek):
1. Open Crossover, Run Command, pick the bottle you want to edit.
2. Type "regedit" and click the run button to open the Windows Registry Editor for that bottle.
3. Find this section: HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer
4. Create a new DWORD Value by right-clicking and selecting new DWORD or clicking Edit, then New, then DWORD
5. Name your DWORD Value "NoTrayItemsDisplay"
6. Set the value to "1"
7. Close regedit and quit & restart Crossover.
You can restore your system tray either by changing the value to 0 or by deleting the entry. On some systems, the entry may show up in more than one place so if at first you don't succeed, make sure to search your registry for "NoTrayItemsDisplay" to make sure you've deleted every instance.