the needs of the books in our primary school here.

Hi, you could check out the books for africa program. Here is their contact form http://www.booksforafrica.org/contact-us.html
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wesley

Here are two resources I was able to find:

This one looks very promising. The organization is Book Aid International and they work with a variety of programs on a local level. Depending on where you are specifically located, they list three possible options (these options are listed on this site: http://www.bookaid.org/cms.cgi/site/our_work/contacts/_tanzania.htm)

Option 1: If operating in mainland Tanzania, a request should be directed to Tanzania Library Services Board (http://www.tlsb.or.tz/) by email (tlsb@africaonline.co.tz)

When requesting book aid, please provide the information:
(*) your organisation's objectives, programmes and/or projects, target groups as well as full contact details including the postal address and country
(*) need: the sort of books being requested, eg vocational materials, medical texts etc
(*) how the books will be used and who will use them
(*) where the books will be placed
(*) whether there are any libraries or resource centres nearby

Also, here's another site that may be able to help you:
http://www.africanlibraryproject.org/contact.html

Hope one of these helps. I'd definitely check with Tanzania Library Services Board first!
-Sean