Basically, RAID using external USB hard drives doesn't look too achievable.
One quote here.
Using USB as the transfer technology
you're only going to achieve a
30-Megabyte or less transfer rate. You
seem to be going to a lot of effort
for a marginal result. For external
use, eSATA is a much better choice for
Maybe I don't understand the intent,
but having 3 USB external drives
working as a single "Dynamic" volume
is almost certainly going to saturate
the Hubs/Controller they are on.
And another quote here.
The overhead of software RAID will
probably cause problems on USB drives.
Even if you get it working I think it
will probably be flaky and error
prone. You can buy USB enclosures that
you can install multiple drives in.
These enclosures use an embedded Linux
so that you can then setup a RAID
array. This way the RAID calculations
and read/writes are all done outside
of Windows. The interface can be USB,
SCSI, eSATA, LAN, whatever, it makes
no difference. Software RAID is a
compromise at best. I don't believe
RAID 5 is supported in Vista in any
case. I would look for a different way
to achieve your goal.
This might be done with dynamic disks. I'm not sure if an USB hard drive can be converted to a dynamic disk, but this seems to be the only way to this. Once you converted your HDDs to dynamic disks you can create all kinds of RAID volumes. If your HDDs' sizes aren't equal, you can still use JBOD, so you can have them all in the same file system.
However, only Vista Enterprise and Ultimate supports dynamic disks.
The biggest downside with an actual RAID is that all the disks involved should be the same size or else it treats all other drives as the same size of the smallest drive. (eg. 2 x 20 GB drives and 1 x 100GB drive) will result in a 60 GB possible capacity - 3 x 20GB)
One of the advantages of ZFS (which has support in mostly server OSes, and not r/w on Windows and only read only by default on Mac OS X) is that you can mix and match drives and it shows them as one pool.