yeah, waqario is right, your another 420GB still exist but changed into unallocated space, you can allocate it as new partition through all the windows operating systems. If you want to resize it, like merge to the copied partition, if you running the windows 7, Vista or server 2008, you can directly through built in disk management to finish. If you running other windows operating system, I suggest you choose 3rd party tool to do it.
Aomei Partition Assistant, which is one of my recommendations:
Its free version, home edition, which is compatible with Windows 7/Vista 32 bit:
http://www.extend-partition.com/free-partition-manager.html
Its pro version, for windows 7/Vista 64bit
http://www.extend-partition.com/partition-manager-pro-edition.html
For server 2008, the server edition:
http://www.extend-partition.com/partition-manager-server-edition.html
Here is an article about resize partition, you can follow its instruction:
http://www.extend-partition.com/resource/partition-resize-windows-software.html