To work in Zimbabwe you need to obtain a work permit. These are usually given to people who are trained in fields that are otherwise lacking experienced personnel. It is relatively easy for UK nationals to receive one of these permits, and they can be applied for through the Ministry of Home Affairs.
Listed below are some useful websites that advertise jobs in Zimbabwe:
4International Careers & Jobs MineJob for mining and ecological job opportunities in Zimbabwe. Search on the International Job Board. Employment Agencies in Zimbabwe. OXFAM also do a lot of emergency work in Zimbabwe and you may find that this is a rewarding way to spend your time whilst in the country.