I recently updated my updated my MacBook with new hardware. I used Disk Utility to "restore" my old drive onto the new drive. This worked great, except that Time Machine uses the MAC address to uniquely track Time Machine backups. Perhaps there is a way to convince TM to use my existing TM backup, but I couldn't find an easy way (if you know, please comment). However, I wanted to preserve my older backups.
This hint provides one method, but I wanted to archive only 60GB of TM data on a 500GB external, and did not want to use the whole 500GB or repartition (which a restore would have required). Most methods of copying TM backups will fail due to TM's hard links. However, in Disk Utility it does work to select the TM drive and choose 'New Image From disknnn.' I saved this as a read-only image on my 500GB external. I could then use this image with TM's 'Browse other Time Machine disks...' feature (after mounting the image, of course).

