A drive must have at least 1 partition. But it may have more.
Go into Disk Management and tell us what it says about both the old and the new drive. What partitions of what size and how many unallocated space? Also please tell your OS (Vista SP1) and the history of this 'relatively modern computer': did it come with Vista or is it an ungraded XP?
http://www.windowsreference.com/windows-vista/how-to-use-disk-management-in-vista/ tells more.
Kees
I have a relatively modern computer with a 250GB Hard Drive in it. It was showing that it was nearly full so I bought another 1TB Hard Drive. I installed it and started transferring files over. After transferring 113GB over it also showed as full. When I right click and select properties for both the old C: drive and the new D: drive. They both show 113GB Capacity when one should show 250GB and the other 1TB. I don't believe either have any partitions on them. What is wrong and how do I fix it?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic