hi every body
i had heared about FreeBSD from a friend but the problem that BSD must be installed on primary partition
i had one primary
one extended(with 5 logic)
i have Slackware in the last logic partition
i want to make a logic partitions to be a primary
i will try fdisk in Linux but i am afraid of losing all my data on the other partition coz they r very important
can any body help?

First, before anything else, take a backup of your important data. This is what you would do anyway; if the data is important, you make sure it's safe even if your systems fail. After that you can start playing around without bigger fears.

Second, I'm not sure what you mean by "make a logic partitions to be a primary"..do you perhaps mean moving the partitions or something? In that case somebody else hopefully has better information..but I wouldn't go there. I would simply back up the data, then create a new partition table - yes, wipe everything out, creating new partitions and formatting them (possibly during the installation of the operating systems). It's not that big a deal if you make good backups, and if you don't, it's your loss - you really should.

I don't get - why would BSD want to be in the primary partition? Any sane explanations?

This topic has come up before in the *BSD forum here. FreeBSD does require a primary partition for installation (see handbook references in that thread).

You should be able to use grub and simply chainload FBSD.

As already mentioned, backup your important files and start fresh.

i am sorry
i didn't understand why it need a primary partition ?