Namibia along with Lesotho, South Africa and Swaziland is a member of the Southern African Common Monetary Area and as such the Namibian Dollar NAD is pegged 1:1 to the South African Rand ZAR. Both the Namibian Dollar and South African Rand is legal tender in Namibia though change will usually be given in Namibian Dollars.
Banks in Namibia will convert Namibian Dollars for South African Rand and vice versa without charge or paperwork. Since any bank or currency exchange outside Namibia including other members of the Common Monetary Area will charge a substantial service fee to change currency, it is advisable to make use of a Namibian Bank before leaving the country.
It is also advisable to carry proof for example, ATM receipts that money you are taking out of the country is money that you brought into the country in the first place.
Rough conversion rates April 2011 are: 6.7:1 USD, 9.75:1 EUR and 11:1 GBP. Current official exchange rates are available from the Namibian Central Bank (http://www.bon.com.na/)
Automated teller machines are available in Windhoek, Swakopmund, Luderitz, Tsumeb, and other towns and cities. It is best to use only teller machines that are inside a mall or other building. Always be careful to make sure no one is watching you enter your PIN, and be vigilant about typical scams e.g. machines that seem to eat your card and won't give it back after you enter the PIN.
Prices in shops are fixed, but prices in open markets or from street vendors are open to barter.
In most towns you will be approached by many locals to buy souvenirs, when this happens a 'no thanks' will usually suffice and they will leave you alone. It is common to haggle. Try to buy as much as possible from small shops instead of bigger ones -- it's the best way to help the poor local population.
The cross-border money transfer facilities are limited and expensive, with one of the poorest currency buying-and-selling rates, because government does not want the money to be sent out of the country. There are no Western Union Money Transfer offices in Namibia.