@Cry:
Does the system boot? What's displayed on the (serial) console?
I have solved the problem. Actually, there was no problem with pfsense but rather with the fact that Windows Vista I am using (don't ask me why) is apparently incapable of displaying any data over serial cable.
After I used a WinXP machine, everything worked fine. The boot-up process was interrupted at a point where you should provide information on vlans and name the interfaces. After that, all the services come up and you can access the webconfigurator through a web client on default IP and password.