I couldn't resolve this. From the documentation, I believe it's a HAL issue, but I was unable to install the correct HAL by performing a Windows repair/upgrade.
I was able to create a fresh Windows 2000 installation in an pre-existing VirtualBox VM - the correct HAL installed okay - but that's fairly useless for what I wanted, which is to virtualize an existing Win2k image.
In contrast, I had no problems whatsoever with vmWare Player. It may not be elegant, but it works. It also had several times the non-VM disk I/O as VirtualBox, so Oracle has their work cut out for them to make VirtualBox anything more than a toy.
Unfortunately, when I ran a SQL Server simulation under vmWare, it was still less than half the speed of the physical equivalent. Another test was a quarter as fast. So I still have to question the deployment of virtualized production database servers accessing external storage.