Go to Control Panel, Hardware and Sounds, Mouse. You touchpad options should be there somehwere. Mine is a Asus laptop and the driver
for my touchpad installs an added tab to control the settings. Have you downloaded and installed the touchpad driver for Windows 7? If not you may have to go to Dell's website and to the drivers
download and get the drivers and install them. If you have done this already then the settings are somewhere in the mouse settings in the control panel. Go to the last tab and see if there is and options or advanced button to click and they may be there. It's hard to help with so little info.