OK to update everyone else, I helped Matt out via MSN and it appears to be sorted.

It appears that the builder image partitioned the drive correctly (all 6 partitions), but did not actually create the ext2 filesystem on the music partition (i.e. the big one - /dev/hda4). I helped him create the file system on the empeg manually from the shell i.e. the root partition and filesystem worked and had all the binaries. Also the swap partition appeared to work fine too. All is good now apparently with both drives fitted. I believe he's synced successfully as well.

I thought the builder broke above 100GB. Perhaps it's >=80GB drives that break it?

edit: I see the Drive Upgrade Guide mentions >60GB drives can cause problems.