For US Citizens, as of June 2003, you only need a valid passport to enter Botswana; you do not need a visa. Be sure that your passport is valid up at least six months after the date you enter the country.
What follows has been taken from the State Department's web site where they list the entry requirements for US Citizens:
Botswana Entry requirements (as of June 2003):
For U.S. citizens, a passport, an onward/return ticket, and proof of sufficient funds are required to enter Botswana. U.S. citizens are permitted stays up to 90 days without a visa. For additional information on entry requirements, travelers may contact the Embassy of the Republic of Botswana, 1531 - 1533 New Hampshire Ave, N.W., Washington, D.C. 20036, telephone (202) 244-4990/1, fax (202) 244-4164. There are also honorary consuls in Los Angeles, San Francisco and Houston. Overseas inquiries should be made to the nearest Botswana embassy or consulate.
Mozambique Entry Requirements (2/27/2003):
Visas are required for entry into Mozambique. It is recommended that travelers have visas prior to traveling. Travelers arriving from a country without a Mozambican embassy or consulate can get visas at the airport or land border entry points for USD 20 or 375,000 Meticais. Those arriving from a country with a Mozambican embassy or consulate can obtain visas at the airports or land border entry points for USD 25. Mozambican authorities impose a fine of USD 100 per day for each day that travelers overstay the period of validity of their visas. These fines can be paid in local currency based on the current exchange rate. Travelers should obtain the latest information and details from the Embassy of Mozambique, 1990 M Street, N. W., Suite 570, Washington, D. C. 20036, telephone (202) 293-7146. Overseas inquiries should be made at the nearest Mozambican embassy or consulate.
Namibia Entry Requirements (June 2003):
A passport, onward/return ticket and proof of sufficient funds are required to enter Namibia. A visa is not required for US Citizens on tourist or business stays of up to 90 days. Persons planning to work (this includes unpaid volunteers) in Namibia must obtain work and residency permits and/or visas from the Embassy of Namibia before traveling. Consult the Embassy of Namibia, 1605 New Hampshire Ave., NW, Washington, DC 20009 (202/986-0540) for further information.
South Africa Entry Requirements (June 2003):
A passport, onward/return ticket and proof of sufficient funds are required to enter South Africa. A visa is not required for US Citizens on tourist or business stays of up to 90 days. It is strongly suggested that travelers check the requirements with the nearest embassy or consulate of South Africa before traveling. Visitors who intend to work in South Africa must apply for work permits abroad at the appropriate South African embassy or consulate. Travelers entering South Africa from countries where yellow fever is endemic are often required to present their yellow World Health Organization (WHO) vaccination record or other proof of inoculation, or they must be inoculated at the airport in order to be permitted entry. Travelers may obtain further information from the Embassy of South Africa, 3051 Massachusetts Avenue, N.W., Washington, D.C. 20008, telephone (202) 232-4400, web site at http://www.saembassy.org, or the South African consulates in Los Angeles, Chicago, or New York. Overseas, inquiries should be made at the nearest South African embassy or consulate.
Traveling to other countries?
The US State Department keeps an up-to-date list of information at http://travel.state.gov/, but if you are uncertain about whether or not you need a visa to enter the country, please check with each country's embassy here in the USA for their up-to-date visa requirements.