Partitioning Drive

I have a 1tb HD and I want to partition it to install another operating system. There is no "unallocated space". How do I go about making my partition?

You won't have any unallocated space until you shrink the current partition.

You can use Windows 7's disk management utility if you wish.

Partition or Volume - Shrink

If you want more control you may want to consider using Partition Wizard, as this tutorial explains.

Partition Wizard : Use the Bootable CD

Basically, you create a Partition Wizard boot disc that you boot into, carry out your partition changes, apply them, and then boot back into Windows when you're done.

so when I shrink it, I won't lose anything currently on my HD?

As long as you are careful, no.

Which operating system will you be dual-booting Windows 7 with?

For example, this tutorial explains how to dual boot Windows XP and Windows 7.

Dual Boot Installation with Windows 7 and XP

well my cousin who works on computers for a living thinks its possible to put the Mac OS on there with windows. my hardware checks out to run Mac well.

You cannot legally install OS X on a PC as Apple's EULA specifically states it can only be installed on Apple branded hardware.

I see thank you for that. Could have landed myself in some trouble.