I was recently working on a Win2K machine and trying to bring its partitions down to one. It had a primary partition holding W2K and an extended partition.

Using Partition Magic I merged the two partitions but got the rather familar STOP message with W2K declining to boot. I put the extra partition back and all was OK again.

I know this problem occurs with W2K (and I expect WinXP) due to a change in the Hardware Extraction Layer (HAL) but can anyone explain...
1. What exactly is the problem that it's complaining about?
2. How can I merge these partitions without getting this problem?
3. How can I fix the problem once I've got it (short of reinstalling W2K)?