Driving from Veracruz to Acayucan can be done via the previous road log / map. You could take the toll road which misses all the interesting attractions of the southern Gulf Coast, or take the scenic route from Veracruz to Acayucan. Either way, you pick up this map at Hwy 180 in Acayucan.
From Acayucan to Escarcega is a pretty straight shot. There is are both toll and free roads. I take the free roads, but most people take the toll road. It will cost around $35 in late 2009 and early 2010.
If you are RV'ing, I highly recommend Freedom Shores RV Park and hotel at Isla Aquada, Campeche. You would turn north at Villahermosa to get there, or if you go on to Palenque, turn back West at Campeche.
You pass the turnoff to Palenque, Chiapas, which you really, really should see.
At Escarcega, if you are driving to Belize, you keep going straight. If you are heading to the Cancun corridor, this will also work.
If you are heading to Merida and the archeological ruins at Chichen Itza, the beach resort of Progreso, Yucatan or to Cancun, Q. Roo, you would turn North here towards Merida.