Make sure you have enough shared memory enabled. This is very limited by default.
Currently (because of issues with the FreeBSD kernel) xine can only play VCDs from ATAPI cdrom drives. not from SCSI drives.
Currently (Jan 2001), FreeBSD-stable (and thus the current releases also) needs a patch to the kernel sources to make VCDs work (please check the FreeBSD documentation if you are unsure on how to build a custom kernel with this patch included).
The file you have to patch is
/sys/dev/ata/atapi-cd.c and the
patch is included in the
README.freebsd file included with
the xine source distribution.