I am guessing that you might be having problems with module support in your custom installation. If you take a look at the manual page ('man apxs'), you'll see the following:
So to use this extension mechanism, your platform has to support the DSO feature and your Apache httpd binary has to be built with the mod_so module. The apxs tool automatically complains if this is not the case.
If you are using the Apache that comes bundled, you might have other problems (on OS X 10.1, at least, module support is already compiled for you). However, if you did a custom build, you might need to recompile with module support, unfortunately....
I recommended to another reader that they try to install another module as well, just to be sure that it is the module support that is failing.
Best of luck,