I upgraded from an old 80gb drive to a newer 125gb drive by dd'ing the first drive to the second drive. I then thought I'd be able to resize the last partition on the new disk using gparted, which I have run before from a Knoppix boot disk. gparted did not show the option to resize the partition however, even though there was a chunk of new space (125 - 80 GB). Can anyone think what's going on here?
What does fdisk show as the partition sizes?
If you dd'd your disk, you will only be able to expand the last partition on the disk.
Changing the partition size is only the first step. You must then do resize (resize2fs) to make the filesystem expand to the new size and make the new space available.