Q: Im in south africa using sa credit card can i change the currency to dollars would it work to get the itunes store

No, you can only buy content from your own country's store - to be able to use the US store you need a valid billing address in the US and be in the US when buying from it.

The iTunes Store in a country is intended only for use by that country's residents, and only while they are in the country. To use the iTunes Store in a country you need a credit card (or other card type if acceptable in a country) issued in that country, billed to an address in that country, and also be physically present in that country when using the store.  You are also restricted to waiting 90 days between country changes.

E.g., "The iTunes Service is available to you only in the United States, its territories, and possessions. You agree not to use or attempt to use the iTunes Service from outside these locations. Apple may use technologies to verify your compliance." - http://www.apple.com/legal/itunes/us/terms.html#SERVICE

I believe there is no iTunes Store in South Africa.  There have been many comments about that here but you'll have to find an alternative service.

Apple has just opened up sales of music in the South African iTunes Store as well as in many other countries.

http://www.apple.com/pr/library/2012/12/04Apple-Launches-iTunes-Store-in-Russia- Turkey-India-South-Africa-52-Additional-Countries-Today.html

Regards.