Unable to use Seemless Mode in OS X Mavricks

[Dantalion]

I just installed Vbox 4.3.28 and newest exp pack on my iMac late 2012. I created a virtual machine to run Win7 for those pesky programs that I must run on a Win machine. Everything installed fine all connections are working but for some reason the option in Vbox for Seemless Mode is greyed out and unavailable. I have listed my comp specs and the Vbox Win7 Specs below. According to everything I have read so far, my graphics proc, CPU, and the amount of Mem I have for both the machine and box should allow me to use the Seemless Mode.

Thanks everyone for taking time to help me out!

Comp Specs:
2.9Ghz Intel i5 Proc
8GB DDR3 RAM
NVIDIA GeForce GT 650M 512 MB Graphics Proc
1TB HDD
OSX 10.10.3 Yosemite

VBox Specs for Win7 Virtual Machine

System:
MOBO: 2048 MB RAM; PIIX3 Chipset; Enabled I/O APIC
PROC: 1CPU; Execution Cap 100%
Enable PAE/NX -NOT enabled
ACCEL: Hardwar Virtualization - Enable VT-x/AMD-V (enabled); Enable Nested Paging (enabled)

Display
VIDEO: Video Mem: 27MB; Monitor Count - 1; Enable 3D Acceleration (not enabled); Enable 2D Acceleration (not enabled)
REMOTE DISP: Enable Server (not enabled); Server Port:3389; Auth Meth:NULL; Auth Timeout: 5000; Allow multiple Connections(not enabled)
VID CAP: Enable Video Capture (not enabled)

Storage
TREE: Controller: IDE ->Empty; Controller SATA ->Win7.vdi
Attributes: Type (Format) Normal (VDI); Virtual Size: 25GB; Actual Size: 10.29GB; Details: dynamically allocated

[loukingjr]

You need to install the guest additions in the Windows guest for seamless to work. You should also change the VRAM setting to 128MB. You should choose the WDDM driver rather than the plain DirectX driver. For the best performance once the guest additions are installed, you should enable 2D and 3D acceleration.

FWIW, you may want to figure out if you are running Mavericks or Yosemite.

[Dantalion]

Thanks loukingjr! I was completely in the dark about the guest additions. I made the changes you suggested and as soon as guest additions are finished installing I will try Seemless Mode. Wish me luck!