5.1-RELEASE installation problem

[Wartan Hachaturow]

Hello.

I've got a 164LX with onboard CMD IDE chipset.
For some strange reason the installer refuses to create or edit
a disklabel on 80Gb Seagate IDE drive. The label utility doesn't
show a "main slice" on which I'm supposed to create partitions.
First of all, I thought the problem may be with one existing large
partition on it, marked as "NetBSD" type (it actually had NetBSD
installed :).
I've booted FreeBSD from another drive, and tried to 
disklabel -w ad1 auto. "Operation unsupported". fdisk is missing.
Okay, I've boot Linux from the third drive. Linux's fdisk recognised
the drive perfectly. I've removed the only partition on the disk,
leaving it blank. Booted 5.1 installer -- just the same, empty label
utility, with no "master slice". 
I tried zeroing the first sector of the drive from Linux -- same
faulty result. I've even tried creating a Sun disklabel with Linux's
fdisk -- this hasn't helped either.
What can be the problem?

-- 
Regards, Wartan.