The hard drive in my Mac Mini G4 is in a rough shape, so I plan to replace it with an mSATA SSD. The HDD contains both Mac OS and MorphOS partitions, and I'd like to retain this arrangement. What would be my best option to clone the contents of whole disk? Is this something can can be done while the HDD is still in the machine, e.g. with a PPC Linux Live CD?

I'm not sure if there are any special tricks to consider with SSD drives (like not writing to all cells which would happen when writing a whole image into it), but in theory it should work by making an image of the whole disk either with dd in Linux, RAWDISK: in MorphOS, or with similar solution.

Here's some documentation if you want to do it by booting from the MorphOS installation media (use the RegisterISO first, as a tip) http://library.morph.zone/Creating_Backups#Cloning_a_Partition_or_Hard_Disk_as_an_Image_File