Thank you! That was totally it!
I just edited my httpd.conf file to inform apache that there are .htaccess files to be read for that directory and things worked again.
I just added:

<Directory "/serendipity">
Options FollowSymLinks
AllowOverride All
</Directory>

and things were bueno again ...

Oh, I forgot to say that I had to manualy type serendipity_admin.php to log in for the first time because all the links (including the css links) were broken too. After I logged in and changed the default theme thoes links began to work. The other links mentioned above still do not work.

Hello,
First thank you for writing and maintaining sweet opensource code!

I am trying to set up serendipity using the beta code (because my I visit my site to maintain it an order of magnitude more then I get visitors) but some of the links go nowhere.

For example I created an article and a ...