Andrea
I'm a novice, and have only owned a Pentax since last December (a K110D), but I have discovered the delights of using cheap old manual lenses. My favourite lens for the past month or so has been a SMC Pentax-M 50mm f1.7 - keep an eye out for one of them!
I operate my M lenses in manual mode, and set the aperture ring manually, but press the AE-L / Green button to adjust shutter speed (but often tweak that again in manual).
Focus is hit and miss, but the AF indicator does give you an indication in the viewer when you hit the target. You may need to press the shutter button down halfway to activate the focus indicator.
On my K110D all that I had to do was set the 'use aperture ring" in the custom settings menu, as my camera lacks image stabilisation.
I couldn't afford new AF lenses, so these old lenses are great for me. There is also a feeling of 'real photography' when you operate that focus ring