Chrome sometimes complains about the Windows installer appearing to be malicious. This is a bogus warning (see here) that I haven't yet managed to fix/work around. If you're unsure, run it through a virus checker first!
Please note that the Windows version requires Windows XP or above (not sure about Windows 8), and hardware support for OpenGL 2.0 or above. If you experience problems you should try updating your graphics drivers. If that doesn't work, you can try changing the value of "SysGlesVersion" to 1 in app.icf (in the installation directory).
If you find PicaSim (or its desktop predecessor SSS) useful or enjoyable, the paid versions on Android and iOS will support its future development, in particular by covering the costs of licencing various pieces of software (Terragen for the panoramic sceneries, and Marmalade for the cross-platform libraries).
So please consider purchasing the Android donation version, the iOS version, or making a small PayPal contribution using the links above. Playing the Amazon Underground version for a very long time will also work!