From talking to DM about this, the DVTU has preset firmware, and not all of the units can be upgraded to bigger drives, tried to replace a DM supplied 320gb drive into a 160gb DS2 and it didnt work, DM's tech support was terrible and offensive, They do offer an upgrade service, but the price is obscene. Now i've ended up here, after buying a segate 160gb drive at the local pc shop, and formatted it via the monitor interface, its all fine
The DM supplied 320gb drive is just a standard hitachi drive, and it booted and worked fine, but didnt last very long before the machine showed an error and froze.
DM do, or at least did, offer a HDD field service training course, and i've done this course.
Hope this is of some help to others.
Big thanks to testweight for the Billy Joel pass