|I am posting from a system I did exactly what you want to do. Trick is you don't do a drive clone but a partition clone.|
It has been three years [lifetime in IT] but I used Ghost to do my cloning. It allowed me to expand the partition. So in your case you would take the 20gig clone partition and expand it to what you want like half the drive. Then do the 2nd drive clone and expand it to use the remaining space.
You MUST do it in the correct order! Drive letters are extemely important since they are stored in the OS registry.
If these are ide drives and you are going to go to sata you have a problem. Cloning is same to same. In other words you boot to ide via ide drivers not sata drivers. This can be overcome by a repair install of the OS which allows you to add the correct drive drivers. You would need to do this for both OS's.