While staying in the town of San Ignacio we hired a taxi driver to take us to Guatamala. He stopped on the Belize side of the border and let us out and waited for us. We shopped at a small market just across the border. I took some video at the market but at the border was a army camp and i was told not to us my camera anywhere around the camp. Very interesting trip.
We rented a Ford Ranger in Belize City and drove along the Western Highway to San Ignacio. It's a little town close to the Guatemalan border. So we crossed to Melchor de Mencos, Guatemala for a few hours to eat some cheap tacos, drink a few Gallo, and buy some artesanias (handicrafts) from the market in the center of town.
There's a definitely difference on the Guate side of the border. There's all kinds of animals wondering about (pigs, burros, horses) that are taking a break from their owners. Food is much cheaper here. Try the licuados (shakes) made with banana or melon. I think a lot of people speak English because it's a border town, and they're probably used to tourists coming over from Belize.