I had the same issue with a Dell Inspiron 910, a MSI Wind, and a Toshiba laptop. All fully updated and running KDE. Fixed it by going to Synaptic and downloading & installing "synaptiks". After installing go to "Configure Your Desktop". On the left menu "Touchpad" will be a stand-alone entry or can be found in "Input Devices" or "Lost and Found". Once found, you can configure your touchpad. Select the "tapping" tab, look about 2/3 down on the right for "tapping with one finger" and change "disabled" to "left mouse". You may have to log out & in for it to take effect. Happy tapping!