It's a pity the original transfer didn't give you the option to use the full capacity of the new drive, or if it did, that you had not become aware of that option.
If the existing C: partition contains a large amount of files that could just be copied to a different location, the simplest solution would be to turn the unallocated space into a drive volume and move the files off the C: drive. If a lot of the space on C: is being used up by downloaded video or music files for example, that could make enough difference that this simpler option will suffice.
If you need to keep the existing contents of the C: drive on C:, the options are more limited, as you cannot expand the C: partition with another partition blocking the way. What is the second 6GB partition for, a recovery partition? Windows XP cannot expand its own C: partition, but if the 6GB partition can be moved to the end of the drive or temporarily copied elsewhere by a third-party partition manager, then the same manager should be able to enlarge the C: partition.
Let us know if either of these options appeal to you, and we should be able to guide you as to the process. Also other helpers might be able to suggest alternative courses of action.
Edited by Platypus, 26 March 2011 - 04:13 AM.