I have an HDD partition problem

Hello,
I bought a laptop but there was only Linux installed on it. I put the Windows 7 DVD and I saw that my HDD was parted 2x150GB (the HDD is 320). I formatted one of them and installed Windows 7. But when I started, My Computer, the other partition was invisible. Then, I put the Windows DVD back and tried to format the second partition from there, but I can`t.
How can I use both of my partitions?
