Here is a road map of Dallas. You can also access maps of Dallas with a free TripIt travel itinerary. To automatically create an itinerary, just forward your travel confirmation emails to firstname.lastname@example.org
Highway 635 acts as the Dallas Beltway. The Western part of 635 is also part of Highway 12, which makes a smaller loop around Dallas.
Driving in from the East or West, you can take IH-20 or IH-30
Driving in from the South, such as from Houston, you can take IH-45
Driving in from the North, such as from Waco, you can take IH-35. IH-35 splits into 35E and 35W just north of Dallas, and 35E will take you into the city, where as 35W goes through Fort Worth.