Windows Vista - 4 Gigs DDR3 Ram showing at 2 Gigs in Vista 64

I have a really weird issue, here are the details.
Firstly, ass stated in the title i do have Vista 64 bit.

Recently bought 2x2 Gig DDR3 1600 (corsair TW3X4G1600C9DH) with
timings 9-9-9-24. My motherboard is an Asus P5Q3 Deluxe.
This chipset (Intel P45) has know issues with DDR3 running at higher
than 1066, but this has supposedly been rectified with a BIOS update
which i have flashed, so not sure if that is relevant as my problem is
not speed related.

Under system properties the ram is shown as 4 Gigs but in task manager
it says: Physical Memory, Total: 2046. The usage graph shows about 1.1
used and is just over half-way full.
Not sure if this is valid but i have a pre-release SP2, not sure if
this could cause such a problem.

CPU-z shows both modules are there, but shows total 4 gigs, however
Everest only shows 2 Gigs.
Screenshot below, hope this is not too big, but theres a lot of info to
squeeze in.

Any help will be most appreciated.

+-------------------------------------------------------------------+
|Filename: Screenie Ram.jpg |
|Download: http://www.vistax64.com/attachment.p...achmentid=8603 |
+-------------------------------------------------------------------+

--
pcbilski