Hi,
Here are two useful links from Jordan Tourism Board:

1. http://www.visitjordan.com/visitjordan_cms/GeneralInformation/GettingAround/BorderCrossings/tabid/105/Default.aspx - List of border crossing. My advice: Either go eastwards across the Lower Galilee from Haifa to Beit Shean, cross the border at Sheikh Hossein Bridge and continue southward in Jordan, or go southward along the Israeli coast, then go to Beersheba, then on the road to Eilat cross the border at the Wadi Araba Crossing (Petra is quite near). Don't use the Allenby/King Hossein Bridge because it is the main gate from and into the West Bank, which means three kinds of authorities (Israeli, Palestinian and Jordanian), more people waiting in line, more forms to fill in and more potential headaches. According to this site, Jordanian visas are issued on the spot at the crossing. Note - unlike the Israeli authorities, the Jordanian authorities insist on stamping the passport itself.
2. http://www.visitjordan.com/default.aspx?tabid=63 - Views of Petra on that site. It is considered one of the most remarkable sites in the region, and the most prominent tourist attraction in Jordan. Jordan is tourist-friendly and quite cheap. Most people can communicate in English. Please note that August falls on Ramadan, so most people you are going to meet in Jordan will be fasting during daylight hours. Be considerate. One more warning - this is August and Petra is in the middle of the desert. Temperature might rise as high as 40 centigrade. Cars, buses and most rooms are air-conditioned, but when you walk outside, cover yourself well with light clothes and drink a lot (but not in front of those who fast).

Dror K