When sysinstall try to detect your devices upon starting up, the
detection could hang up if:
  - the kernel contains one of the network interface driver tried to
        loaded at startup time
  - on device detection hangs

So you can get a warning messsage when you select CD/DVD media, that
No CD/DVD devices detected in your machine... 

we don't know wheater only this case can fool deviceGetAll() from
devices.c or a buggy hardver too.

Fix: 

For the network interfaces is simple: don't compile it into the
kernel, but if bogus hardware present the hangup, try to remove it or
disable it from bios while installing.
How-To-Repeat:        compile and build an install CD from /usr/src/release/sysinstall,
and compile and build a kernel with one of the drivers sysinstall load
at startup. Try it to install.

When sysinstall starts, you will get an error message, that if_* could
not loaded up. After the Detecting devices, please wait... message try
to set the media to CDROM, and you should get the error...