I thought of that, but I was hoping that it would be possible without disassembling two computers.
If you don't mind the additional expense, you could snag a firewire enclosure and put the old drive in that. That's what I did when I upgraded my TiBook to a 48GB internal - I used the old 10GB drive in the external firewire enclosure for transferring files for several months until giving it to my sister, who was suffering with a 6GB drive on her Powerbook.
My Mac doesn't have FireWire; it's an old beige G3. I could possibly get a USB enclosure (I've put in a USB card), but that'd be dead slow. Though I could do with just one disk, if I can move everything (metadata, hidden files and all).
Your proposed plan seems quite sensible, and surely only involves opening one computer (assuming you've already swapped the 40 for the 10) - or have I missed something?
I already pulled the 10Gb disk out; that's taken care of.
Actually, I just copied files across now and have the 10Gb disk in the Mac. Except that all my preferences/software registration information has been lost (and needs to be reentered). I take it MacOS doesn't keep that in files.
Mac OS does keep registration data in files, but many applications make that invisible. If they put the invisible files in a folder (the System Folder is popular), then of course the registration information will get copied when you copy the entire folder. But if they put them in the root of the drive, there's no easy way to select them to copy them over, without making them visible.
Also, some programs store hard disk size and other system details in their registration files, and intentionally "forget" their registration if they think you have moved them to another computer even though the registration might be valid otherwise. This is technically known as a "pain in the ass."
And then there's the PACE stuff (as used by Cubase VST and such), which is kept somewhere outside of the partition proper (apparently between it and the next one).
I've heard that if you have a dd-like program, it's easy enough to back up/restore PACE authorisation. However, even thinking about it is probably a felony under the DMCA and other WIPO-treaty-related laws, so don't do it kiddies. Prison is not a nice place.
This might be a little easier than doing the switch game with the CDROM. Take the 4 gigger out of the old mac and put it in your Linux box. mkhfs(or whatever the equivalent is), then copy the files over and put the 10 gig drive in the old computer. You could also try a dd from one drive to the other.
The kernel will have to recognize Mac partitions and you'll have to have HFS_tools installed.
If you want to do it under OS 9, I'm sure someone has ported 'dd' to Mac..