Google’s often accused of endangering Windows with its numerous cloud-computing projects, but the search giant also seems intent on replacing bits of Windows itself.

I download the beta of Picasa 3 at the weekend, and at the end of the installation was offered the chance to install something called Picasa Photo Viewer – which basically replaces the Windows Picture Viewer with Google’s very own alternative.

Now when I click on photos in My Pictures or JPEGs attached to emails, I’m presented with the screen below:

The first thing that strikes you is how very Mac-like the Picasa Viewer is, with its transparent window and smooth-scrolling slideshow and thumbnail options. It’s almost as if Google is trying to embarrass Microsoft by making Windows look better than Microsoft does.  

What’s Google’s motivation for replacing Windows components with software of its own? Yes, there are prominent links to upload and edit photos in Picasa, helping to keep users within Google’s walls. But I can’t help wondering if Picasa Photo Viewer is designed to remind us – and Microsoft – that Google’s more than capable of  designing operating system-style elements, too.

Is that much vaunted Google OS really just a rumour? That’s what they said about the browser…