DSL comes with libstdc++5. You may be able to get this package (https://archive.debian.net/sarge/libstdc++6-dev) to install, even though it is for a later version of Debian than the one DSL is based on, by manually installing other dependencies.
It may be easier to compile libstdc++6, which part of the GCC compiler (http://gcc.gnu.org/gcc-6/), from the source code.
Remember to also check the other dependencies that the program you are trying to run requires. It is possible that it may require a later Linux kernel than the 2.4.31 version used by DSL, and this will make it incompatible. If so, you may want to check past versions of the program before moving on to other alternatives.
EDIT: Sorry, as for apt-get (even though it won't help you anyway, because there are no libstdc++6 packages for Debian Woody), you can download the dsl-dpkg.dsl MyDSL extension to enable it from the "System" section of the MyDSL respository (http://distro.ibiblio.org/damnsmall/mydsl/).