You're fine. Windows is installed in Legacy/Bios mode on your machine.
There are currently 3 primary partitions. The limit is 4. That will
not be a problem. Only thing you should do is defragment the partition called "C:" drive in Windows before installing LL.
As a precaution, backup anything important and make Windows recovery DVD's if you don't already have them.
Then you have a choice:
1. Run LL installer, pick "
Alongside Windows" when you see the choice on "
Installation Type" screen, and shrink the Windows partition on the next step.
OR
2. Boot LL DVD and use a program on the live Linux disk to shrink the partition. It's under
Menu -> System -> Partition Drives. The program is called
GParted and there is a tutorial showing how to use it here:
http://www.dedoimedo.com/computers/gparted.html. Shrink partition first, then close GParted and run the installer.
Which ever way you choose, try to make at least 20GB for Linux, but don't shrink by so much that Windows has no room for expansion. Look in Windows disk management before you run LL installer to see how much of that C: partition is being used by your files. (Picture shows it is 454GB, but can't see the "used" column.) Determine how much you are going to allot for Linux based on the room you have left minus how much extra room you want to leave for Windows.