Please reference https://bugzilla.redhat.com/show_bug.cgi?id=431915 comment #5 for details.

Description of problem:
In order to network install Fedora or RHEL onto a blade whose NICs are configured with a native non-routeable network, but a routeable VLAN, the VLAN tagging must be added to the initial kickstart file.  However, while the 8021q.ko module has been added to the initrd, anaconda and pykickstart still don't utilize the 'vlanid' parameter.  Could we please add this?

Additional info:
The initial kickstart (and subsequent final ks) would include something like:
label newdiz
  kernel vmlinuz
  append ks=http://rhelinstall.obfuscated.org/server/software/os/linux/rhel5.5/64bitks_newdiz.cfg initrd=initrd.img latecfload noipv6 ip=192.168.48.17 netmask=255.255.255.0 gateway=192.168.48.1 dns=192.168.160.160 vlanid=848