How can I make an image slightly transparent?

like in this one https://tools.google.com/chrome/intl/en/

I want it to have colour, but the colour should be like see-throughish, kinda.

I have Photoshop CS4

I remember doing something like this in Flash once, where I made the image lose some transparency but not all...Any advise please?How can I make an image slightly transparent?
Have you checked filters?How can I make an image slightly transparent?
You need to alter the opacity of the image of want to make transparent.



The opacity thingy is in the same box as the layers.