You can have more than one Primary partition. Are you saying you installed Windows 7 on the 10gb partition by mistake?
Go into Disk Management and post a screenshot of the drive map so we can advise you, using the Snipping Tool on the Start Menu, attaching file using Paper clip in reply box.
Chances are you can click on the partition and Extend it to the right. If there is something blocking that, then delete it so you can extend your Win7 partition as far as you want.
Otherwise, boot into the Win7 DVD, choose Custom install, Advanced Drive tools and delete all of the partitions, create partition(s) you want carefully this time, and make sure the partition you want to install Windows 7 is the one highlighted when you click Install.