Try installing the latest version of the touchpad driver, available from Synaptics.
I installed it last night on my laptop, and after restarting, there will be a whole host of new options at the bottom of the list. The option that you are looking to disable is the one that allows you to swipe from off the right edge of the touchpad to the center - that is what is activating the charms.
The feature you're looking to disable in the Synaptics driver settings is "Enable Edge Swipes". The image below is the settings for the driver version
The the description from the help text:
Enable Edge Swipes
Select the Enable Edge Swipes checkbox to enable a one-finger movement from the edge of the TouchPad in towards the center of the TouchPad:
- A swipe from the left edge to the center switches from the currently open application to the previously open application.
- A swipe from the right edge to the center opens or closes the Charms bar.
- A swipe from the the top edge to the center opens or closes the Application Bar.