The bus terminal is west of the city center (it was moved there from To Chau on the other side of the bay around January 2008). There are buses from Ho Chi Minh City's Mien Tay terminal (about 8h) as well as from Can Tho and Chau Doc. The connection from Can Tho often requires a change in Rach Soi or Rach Gia from where it is about 1h.
The border near Ha Tien (7km to the north) was opened for tourists in 2007. As of late 2010, it is possible for tourists of most nationalities to enter Vietnam via this border crossing without the need for a visa. However it applies only for stays of up to 15 days, and you can only visit the so called "Special Economic Zone", which is essentially the town of Ha Tien, and the area between the town and the border, including Mui Nai beach. You must not travel further into Vietnam. (The officials at the border will tell you that you cannot go to Phu Quoc island with the visa and may not issue you a visa at all without a small bribe.) For ventures further into Vietnam, a visa is needed prior to arrival at the border.
To get to the border from Cambodia you can hire a motor bike taxi from Kampot ($10), Kep ($7), or Kampong Trach ($5). The road can vary in condition from paved and bumpy to packed dirt and bumpy, be prepared for a slightly white knuckled ride depending on the daring nature of your driver and the road can also be very dusty in the dry season. Also, be aware that there seem to be Vietnamese drivers now waiting well inside the Cambodian side waiting to pickup (poach) prospective travelers to take them across the border into town. Your driver may stop here to talk with them and seem to suggest you go with them. A ride to town should be $3-4 or less (it is only 7 km and the road is well paved on the Vietnamese side.) If you can't agree on a price there you can simply have your Cambodian driver take you to the border where you can cross over and have the drivers on the other side fight over you
