3 partitions created when trying to partition an external hard disk into 2 parti

Hello,
When I tried partitioning my new hard disk (where I have already started copying files into before realising that I should have made a partition) it resulted in 3 partitions instead. I used the disk manager/utility on Vista and I only wanted to make 2 partitions. It did ask me how much I wanted to shrink the original hard disk by. The hard disk was a 3TB and I wanted to shrink by approximately 1TB. Instead of creating a primary partition and an unallocated space for the second partition, it created sub-divided the unallocated partition into 2 separate unallocated partitions (1 approximately 0.25TB and the other 0.75TB). The disk management utility allowed me to format the 0.25TB (which was next to the primary partition) but did not allow me to touch the 0.75TB portion/partition of the hard disk. When I right clicked on it, all the menu selections have been greyed out. If 0.75TB were to be lost just to maintain the partitioning of the original 3TB hard disk, I would not prefer having the partitions at all. Is this 3rd partition (or unallocated space) cannot be used at all? If so, can undo what I just did (i.e. merge the primary with the other two unallocated spaces to make back the approximately 3TB usable space without having partitions). Thank you for your help.