By car
Grapevine is more or less equidistant from both downtown Dallas and Fort Worth. SH 121, 114, 360 and IH 635 all converge in Grapevine the "funnel".
By train
Right now, the only rail to Grapevine is the "Grapevine Vintage Railroad" that runs between Grapevine and the Fort Worth Stockyards. More of a tourist attraction than anything else, too slow to use as transit.
Also, DART Dallas Area Rapid Transit has plans (http://www.dart.org/about...) for a new light rail line orange through Irving and ending at DFW airport. Although it won't travel into Grapevine, it will probably have a park and ride just outside the city limits on the north side of the airport.
By plane
Just north of DFW airport - therefore easy access by air. Most larger hotels have their own shuttles to/from the airport.