That's my understanding, Sandra, that dynamic drives can be used with XP Pro and Vista Business/Ultimate.
But the drive can be seen with Vista Home Premium (but not XP) and I used Vista Home Premium to convert the disc from Dynamic to Basic, with Primary partition (using Disc Management). It then worked with XP and I could send files to and from the disc. (As I'm writing this, I remember - whether it's relevant or not- I had to manually set the 'send to' command, I think in Vista but not XP!).
Now for a few more details on the problem, which I appreciate I didn't explain explicitly:
I managed, eventually (after a few attempts), to load Vista Home Premium in dual boot arrangement using the 'free' Upgrade disc supplied with the MD8818 (doesn't need activation/serial) on the new hard disc. (I installed from XP, as it 'fixes' drive designations and automatically sets up 'dual boot').
In Windows update, there were 96 'important' updates, so I proceeded to install and never succeeded after umpteen attempts. I saw a plethora of seemingly misleading error messages both software (NTLDR missing, Black Desktop, Corrupt Registry, Need to install important update etc) and hardware (Memory, Disc). Trying to install SP1 failed, as it needed some important updates beforehand.
In XP mode, there are no hardware issues.
Had to resort to using Vista 'Repair' several times to get Vista to boot and to restore- until finally it gave up, saying 'could not fix PC'.