first you will need booking confirmation for a prearranged guide for Algeria.
However, as fas as I know Algerian visa are not issued in Mali if you are not resident there. Same for Niger, but at least in the past tourists were able to get a 7 day transit visa in Agadez. I know of only one case in the last 3 years that a transit visa had been issued in Gao, Mali but this was probably an exception because the tourist had an expired visa in their passport. Actually I would not take it for granted to get a transit visa in Agadez or Niamey.
BUT - all governments strictly advise against travels in northern Niger and Mali because of the very high risk of kidnapping and banditry (exhaustive info about is available on the hubb). The thread is really serious (I travelled in Northern MAli and Adrar des Iffoghas in 2005 and 2007 but certainly consider by far too risky, even with a reliable guide).
Last edited by Yves; 6 Mar 2011 at 19:42.