Can I use the lenses from my old Pentax ME super 35mm SLR camera with a digital SLR?

I have a Pentax 50mm lens, a Sigma 70 - 200mm and a Sigma 500mm lens. They are all manual focus. I believe the mounting type is a Pentax K mount (bayonet fitting). Could I use them with the Pentax ist or somthing similar?

Yes you can.

If they are "A" series (an A on the aperture collar) you get full function (except autofocus). If no "A" then they are called "M" series and you can still mount and shoot, and have what's called stop-down metering

A lot depends on the camera.

The basic K Bayonet has been upgraded by Pentax etc to incorporate auto-focus.

Some Digital SLRs will still allow you to use these lenses, but you need to check the exact model: New Bayonets Are Kaf Kaf2 and Ka, all of which add advance feature such as auto focus, and aperture control.

Your manual probably has a page - very near the back - showing which lenses are compatible and which features will or will not work.