There's a number of opportunities for those looking to volunteer in Zambia. While various international agencies offer roles in a number of fields, you can try the following places based in Zambia:
Chimfunshi Wildlife Orphanage Offers several roles managing day-to-day affairs at this chimpanzee refuge; get in touch with African Impact (www.africanimpact.com) which coordinates affairs here, as well as other volunteering options in Zambia.
Game Rangers International This wildlife NGO offers a range of different opportunities through its volunteer program; check its website for upcoming placements.
Habitat for Humanity Helps to build houses for the nation’s poor; over 2700 houses have been built since 1984.
Tikondane Community Centre A wonderful grassroots organisation assisting with local communities; it accepts volunteers to help out with anything from teaching, agriculture and permaculture to health care. There's a minimum of two weeks and it costs ZMW2000 per week, inclusive of meals and accommodation. It's based in Katate in eastern Zambia, located between Lusaka and South Luangwa National Park.