I use VirtualBox on Mac OS. Windows guest, Mac OS host. On the Mac, the keyboard layout is a bit different: While on the PC the three first keys in the last row on the keyboard are Ctrl, Windows and Alt, the Mac has Ctrl, Alt and Command. From the key code perspective, Command and Windows are the same.

The problem is now that the Windows guest gets the key codes, i.e. Alt and Windows are swapped. Of course the label stays, the same, but if you type blind, this doesn't matter. So to use Alt+Tab (to switch between different windows) one needs to press the second key, not the third key. Maybe some people like that behavior, but I don't. There are feature requests, but VirtualBox developers don't want to implement it.

So I decided to look for a solution inside the VM. There are many tools in Windows to swap keys, but most of them are way too overloaded. Searching around in the web, I found a much simpler solution which consists only of adding a value in the registry.

There's a so-called Scan-code mapper for keyboards described in the MSDN documentation. All you need to do is to add a value called HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Keyboard Layout\Scancode Map with following value:

00 00 00 00  00 00 00 00 
03 00 00 00  38 00 5b e0
5b e0 38 00  00 00 00 00

After that, just reboot. No need to install tools, no autostart. If you want to get rid of the behavior, just delete the registry key and you're done.