IIRC you're connected to the serial console of the guest, so if your software isn't setup to use the serial port nothing will happen (or output only garbage).
I found instructions here
http://blog.zelut.org/2010/05/05/configure-serial-console-access-on-centos-5...
and it kinda works - I can see the start of the boot process, and once finished, I can login via serial console, but do not see the boot output. Still, better than nothing.
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