Hey, on earlier versions of Photoshop there was a Transparency Tool in the top right corner, it was a very basic tool where you clicked on the layer, and there is around 50 different transparency percentages. The transparency tools should be where Colour, Swatches and Styles are in the top right corner. Does anyone know where to enable this tool (If CS4 has it)?
I think he meant the opacity value in the layers palette. The last 3 versions of PS added the Fill percentage. But the more versatile and complete Blending Options (when you double-click a layer) allow you to create some interesting effects; for exemple by very simply moving a few sliders while holding the Alt key. You can also decide which color components are affected, etc. (advance blending area).