it seems as if the webapp module for apache does not handle the [PT] ("pass-through") parameter in rewrite rules correctly. instead of handing over the rewritten request uri to tomcat (and in consequence to the embedded servlet application), the uri is processed by apache itself... which lead to a lot of 404 server errors on my machine.

anyway, i succeeded with defining working rewrite rules that do pass-through the result using another method that actually is described in the tomcat 4 docs in the section "the ajp connector". unfortunately, not a very obvious place and very far apart from all that warp engine mumbo-jumbo in the first and overall sections. here, the jk module of version 3 is acting as software bridge between apache and tomcat (works perfectly, even with version 4.0.1).