Hurray! I just realised that my larger external hard drive enclosure takes a SATA drive, so I can use the existing 500Gb drive to replace the 250Gb drive in my iMac, then install a new 1.5Tb external drive for backup.
Why do I need more space? Simple – I just installed the entire Logic Studio set, and lost about 50Gb of hard drive space on the internal drive.
Hrmm. I should probably try to find a larger IDE hard drive for the other external drive. 300Gb just isn’t very much space anymore. That or a SATA-IDE adapter. Or… maybe put that 1.5Tb drive into the Time Capsule and use it for all the backups? No.. too dangerous to put all the backups on the one drive..