RAID-1 with different sized disks under vista, intel matrix ICH9R

I have an ICH9R board and intel matrix storage. I previously had a 1TB
drive with 250GB free (not partitioned). I added a second 250GB hard
drive. Is it possible to create a raid1 volume (end of 1TB drive+full
250GB drive) without loosing all my data on the other 750GB of the
drive? I don't see how to do it in the matrix storage console.
I know it's possible to do this with software raid but vista doesn't
support software raid-1.

If it's not possible, can I backup my data, create a 250GB raid1 array
in the BIOS, and create an other 750GB partition during vista setup for
less critical files?

What purpose is this raid going to serve? I trust its not in place of a
backup strategy.
Usually its data partitions you would want to mirror
You might, depending on why, be better off using an Imaging app to backup to
your new drive

Simple : I want two volumes : one 750GB for non-critical data (games,
movies, etc.)
and one mirrored (raid1) 250GB volume for my documents and pictures.

I have two disks : 1TB and 250GB.

Is it possible to do this with either vista software raid or intel
matrix storage?

You would need to ask Intel if their chipset and driver support this
functionality. I'd guess not.

You could probably get away with different make/model, but absolutely they
have to be the identical total capacity to be used in RAID configuration.

I know that I can use different sized disk in a raid array (at least
with intel matrix storage). What I don't know is if the remaining space
can be used or not.

If I was in linux I would do this with mdadm in a few seconds.

No it cannot. If you set up a mirrored array with one 250GB and one 1TB
drive, you will loose all but 250GB of the TB drive.

If you like software RAID, you can do the same in Windows in just a few
seconds too.

No, vista doesn't support RAID1 or RAID5, only RAID0.

RAID support is determined by the motherboard. My VISTA supports
RAID 0, 1, 0+1 and 5.

If you're using hardware based RAID, this is true. Software RAID
availability is determined by the OS, not anything in hardware.