Yesterday I changed my 4 GB harddisk for a 20 GB.
Although I couln't really find any info on the internet, and after listening to Apple Help line guy (Netherlands) telling me that I should just add an disk in my iMac Bondi Blue (rev A) I cried for a while, went to the very first ordinary peecee shop and bought a Seagate IDE ATA 100 disk, swapped it (after burning several cd's as backup) and placed everything back on it.
Took a while, made two partitions (15 and 5), but for an until now unknown reason, I cannot boot from the second partition.
Any help / explanation about this would be appreciated, and if I find it out myself I'll post it here.
Disks are quite cheap, so I wouldn't even consider an usb-based harddisk, even if speed isn't the issue.