Go to Google Maps, click "Get Directions" (right under the logo at top left), enter these two addresses:
5085 Westheimer Rd., Houston, TX
2600 Highway 6 S, Houston, TX
...and then click the "Get directions" button. This will show you a route from the Galleria mall to West Oaks Mall. UNFORTUNATELY... the route it shows will put you on the Westpark Tollway. My friends, this is no ordinary tollway! It is an EZ Tag Only route. There are no booths for accepting cash; you MUST have an EZ Tag to drive on the Westpark Tollway. If you drive on it without one, your license plate will be photographed and you'll receive a ticket in the mail. The purpose of the tollway was to alleviate congestion on Westpark Drive, and the two roads run mostly concurrently. But apparently, Google Maps doesn't know about the EZ Tag Only thing!
(Anyway, see Westheimer Rd., which runs directly between the two points? If you don't have an EZ Tag, that's the best way to go.)