Unable to write to disk during installation

[Mattia Popolla]

I'm trying to install FreeBSD/i386 5.3-RELEASE
FROM A DOS PARTITION.

I have two HD units, with no partitions:
Primary master - C: - ad0 (the "primary partition")
Secondary master - D: - ad2

I copied the distribution in C:/FREEBSD.
Booting FreeBSD from floppies I get some error messages,
like these:

ad2: FAILURE - READ_DMA status=51<READY,DSC,ERROR> error4: aborted   LBA 1
ad2: FAILURE - READ_DMA status=51<READY,DSC,ERROR> error4: aborted   LBA 1
ad2: FAILURE - READ_DMA status=51<READY,DSC,ERROR> error4: aborted   LBA 2
ad2: FAILURE - READ_DMA status=51<READY,DSC,ERROR> error4: aborted   LBA 1
...

During standard installation I choose to
devote all space in unit ad2 to FreeBSD.
But installation fails in the last step
showing these (expected) messages:

"ERROR: unable to write data to disk ad2!"
"Couldn't make FileSystems properly. Aborting"

Unit ad2 is an old 1624 MB Western Digital HD
(model WDC AC31600H, PIO MODE 4, no ULTRA DMA)
but IT IS NOT FAILING, all the clusters are OK,
and it works perfectly with MS DOS/Windows.
I've also freshly formatted it using the MS-DOS FORMAT command.

Can this be a driver problem?
The other HD (unit ad0) seems to work,
but I can't make partitions in it!
What can I do? Please help me!!!

Thanks for your support,
and sorry for my bad english!