[syslinux] [extlinux] mbr.bin starts windows?

[James Rhodes - I am everywhere.]

I'm trying to install extlinux on my dual-booting computer, but when i try

cat mbr.bin > /dev/sda

the computer boots windows (it doesn't even come up with the extlinux
menu).  My partition setup is as follows:

/dev/sda1 -> NTFS (Windows)
/dev/sda5 -> Linux Swap
/dev/sda6 -> Linux Root (/)
/dev/sda7 -> Linux Home (/home)

Now I presume that mbr.bin calls the bootsector of the first
partition, but I want it to call the bootsector of the 6th partition
(in an extended region).  Is there anyway to make the mbr.bin file do
this?