The xplane python plugin has its own python2.6 built in to it. It needs some
modules (in *.so form) that are in standard debian squeeze python2.6 built
in to the python binary itself. Thus the python2.6 debian package does not
include those *.so modules. One such module is math.so. It has all the basic
mathematical function (such as sin, tan).

The get the math.so module do the following:

>su root
>mkdir xpython
>cd xpython
>apt-get source python2.6
>cd python2.6-2.6.6 (or similar)
>./configure

If configure complains about missing libraries, you must install the
*-dev versions of those libraries.

>make
>cp build/lib.linux-i686-2.6/math.so /usr/lib/python2.6/lib-dynload/

If your xplane python plugin complains of some other missing .so
copy that as well.