have I been hacked already
The reported lines are probes for software with known vulnerabilities like PHP's XMLRPC handling. If you don't run any of that software, or if you *made sure* you run *verified safe* versions (updated to latest), these probes should not have been successful, and the 4xx and 5xx errorcodes provide positive indication of that. This does not mean there are other vectors of attack (for instance because it does not get reported). Please make sure your host is hardened properly, you update your software regularly, audit the box regularly and that have accessable software properly ACL'ed (daemon configs, Xinetd, TCP wrappers, firewall) where applicable.
Please check out the
LQ FAQ: Security references for more.