Is any documentation available on howto install jsMath with moodle?
Yes, there is a README file that contains the installation instructions. See the jsMath filter CVS site.
Will jsmath coexist with the moodle algebra filter?
I've never used the algebra filter, but it should not be hard to use them in conjunction with each other. You will need to set the configuration of the jsMath filter so that it will use characters other than the ones used by algebra filter to indicate the start and stop mathematics. By default, jsMath uses \(...\) or <tex>...</tex> to indicate in-line mathematics and \[...\] or $$..$$ to indicate display mathematics. If the algebra filter uses these, you can set them to something else in the jsmath/javascript.php file and jsmath/filter.php files.
The jsMath filter is not listed o the moodle filters download page... Is there any reason for this?
The jsMath filter is one of the user-contributed filters, of which there are several dozen (see the contrib CVS site). Only the official filters and modules are listed on the download page.
Davide