Ok but better start anew, so
1) remove Mathmap
2) Open the Gimp folder, not Gimp but its folder with explorer and type there the name of that dll
in the screengrab , framed in red the SEARCH field where you should type the dll name
In the pic is also my result , i too have more then 1 dll, that is normal because other plugin as gmic uses the same dll but in a 64bit version, but everything works because the 32bit dll required by mathmap is not floating around but in a dedicated folder with mathmap exe and the other MM dll ,( same for the versiion needed by gmic )
3) i believe this the most recent and complete build of mathmap
http://downloads.sourceforge.net/project/gimp-packagers/MathMap-Zip-Install%281%29.zip?r=&ts=1388694049&use_mirror=nchc The difference is that are much more filters then in the last official build (for the rest are no changes )
4) then are also instrution inside the zip, that anyway are the same then comboguy posted
you have not to move many files but only 2 folder that you will find in the zip "plugin" and Mathmap"
And to make life easier you MUST not to extract files from "plugin", move the whole folder inside gimp "plug-ins" and the other folder "mathmap" folder just inside your gimp user folder.
Loading gimp nothing will happen because a last step is needed
in gimp click Edit/ Preferences/Folder , expand "folder" and chose plug-ins, there click the "new folder" icon and then "..." (yes "..." ,stand for search)
a file explorer will pop out, just indicate the "plugin" folder with MM , click okey
Done! Next time you load gimp MM would be in Filter/generic