Difficult - the pronunciation of a Chinese name can change dramatically from one province to another.
If you check this wikipedia article -
http://en.wikipedia.org/wiki/Common_Chinese_surnameYou may recognise no.32 on the list as your Tsang, apparently the Hong Kong version in the Roman alphabet. I'm guessing here, probable Mandarin pronunciation something like DZEUNG, probable Cantonese pronunciation something like DZAHNG.
You can also find an article on the name Zeng (pinyin spelling) on wikipedia.