In order to use the jsMath for displaying mathematics with TeX Drupal 6.x module you need:
You want to install the files of the jsMath module in the usual 3rd party module folder. This folder is generally:
<drupal path>/sites/all/modules
When extracting the tarball, you get a jsmath folder with the module.
The jsMath library can be installed in two different locations, one is mainly for backward compatibility.
New installation should put the jsMath library in the libraries folder as in:
<drupal path>/sites/all/libraries/jsMath1
The jsMath module automatically checks for the jsMath folder in that libraries directory. If it is present, then it is used.
The other folder is under the jsmath folder. The reason why that folder should not be used is because Drupal scans all the folders and sub-folders defined under modules. Any file with the .info or .module extension will be discovered and loaded in some way. That could generate incompatibilities in the future. The exact folder is this one:
<drupal path>/sites/all/modules/jsmath/jsMath1
Note that the jsMath library folder name has a capital M.
jsMath can be used with additional, complementary fonts. These fonts need to be installed on your server. These are TeX like description of characters that the JavaScript processors uses to generate the characters. The library can also use picture fonts. Those have a drawback, they do not resize very well at all.
All the fonts go under the jsMath/fonts directory. Each font is defined in a folder. For instance, the cm-fonts or the cmmi10 fonts. Depending on the font file that you use, the structure may be slightly different. Make sure you get the font at the right location.
Now that the jsMath module, library, and optional fonts are installed, you are ready to enable the module. Go to Adminster » Site building » Modules and enable the jsMath module.
Now the module is ready.
The jsMath settings are found under Administer » Site configuration » jsMath2.
The different options are very well described and I assume that you know something about TeX already.
Although previous versions of jsMath would not require the use of an input filter, since version 2.x, to avoid security issues, jsMath is only available via an input format. For this reason, you need to edit one or more of your Input formats and install the jsMath filter to the Input format that you choose.
Input formats are defined under Administer » Site configuration » Input formats.
Edit each format that should support jsMath and select it there.
At this time, the jsMath settings are all in the global settings window. Filters have no additional settings.
IMPORTANT: Choose wisely. This filter is considered to be similar, in dangerousness, to the Full HTML filter. For this reason, you want to only offer access to this filter to trusted users. You can read more about the jsMath security issue on the page created to this effect.
I am thinking to add an additional two features that will impact the installation: