"mmmmmm...... cherry pie"

(Liam reference)
I finally got to play around with this a bit and as the instruction on that site mentions, size of drive does matter.....to a point.
I used chdman32.
Seems it really all depends on what size the drive is that the CHD was created from. (like you had mentioned)
Liam's image came from a 20GB drive, so it should be dumped to a 20GB or slightly better drive.
I took his image and dumped it to a 30.7GB drive twice without a hitch, worked perfectly. But anything much bigger than that gave me fits. (I only had a 60GB and 120GB handy, both were Maxtors)
I then created an image from the original 40GB drive that was in my machine and it absolutely would not dump to a smaller (30GB) drive. Wouldn't work on the bigger drives either, would write to them fine, but wouldn't work in the machine. I don't have another 40GB drive around to try my image on, but I created an image twice and they came out identical in size.
All the failures I had gave me the same "could not mount" type error you had. (Error 6 or whatever, then reboot)
The "hunk" numbers proved my point....there was almost exactly double the number of hunks from my 40GB drive versus Liams 20GB drive.
And when my 40GB image would fail trying to go to the 30GB drive, the numbers were proportional to the missing space it need. (that extra 10GB)
So obviously the CHD images take into account for data "space", not just the data itself. (otherwise the images would be teeny if it was "just" data)
Oddly the CHD I made of my drive is smaller than Liams.....I don't quite get that.
His was 1.61GB and mine was 1.52GB even though my original drive was bigger. (?)
So now the quest is to figure out how to create a small enough image to dump this to a smaller CompactFlash drive. (inexpensive size that is)
That 10GB CHD image would be a good choice to start with.
Would be nice to find a CHD image from say a 2GB drive if it exists. I know a Megatouch Titanium is barely 850MB, figured these Infinity games weren't much bigger than those data wise.
By the way Liams version is " 2.03c NJ " mine is " 2.03b ".
I think the NJ versions have some minor difference in pricing and such due to different regulations in New Jersey. Or something to that affect.
Also learned all the highscores are saved directly to the drives....
This was the first time I had ever messed with chdman, so it was kinda cool just to toy with it a bit.