WINDHOEK, Namibia -- Microsoft Corp. sees sub-Saharan Africa, among the poorest places on earth, as one of the last great computing frontiers. It wants to make its Windows software a fixture there.

To that end, it has established a presence in 13 countries, donated Windows for thousands of school computers, and funded programs for entrepreneurs and the young. It also has used aggressive business tactics, some aimed at its biggest threat in the region: Linux, a Windows alternative that costs little, and sometimes nothing at...