Is it possible to install PC-BSD on an extended partition?
No. PC-BSD can only be installed on primary partitions. Unless you are planning on using the entire hard disk, your partitions need to be created prior to starting the installation. This means that if you want to create multiple partitions or install other operating systems, you will need a third-party partition manager. If Windows or Mac OS X is already installed, you can use their disk management utility. You can also use an open source utility such as Parted Magic.