you can manage your partition with windows disk but that will format your drive so backup your data before doing so. so you will boot from the cd...click install windows...advanced and from there you will see a list of logical drives meaning each partition will look like a drive...click on each and do format until you will see a single partition and then install windows on the single partition
Well if you're going to install Windows 7 on it, presumably from a Microsoft DVD, you can boot from that and it has the built-in ability to delete and create partitions before it installs Windows.
Just boot from it, wait until it presents a screen showing you the existing partitions, and follow the on-screen instructions to delete each partition.
That will leave the drive with only "Unallocated Space" (no partitions at all).
Just follow the prompts to install Windows on that unallocated space and Windows will automatically create a new partition there, then it will format it before installing Windows.