your windows is only seeing 3gb because you are running a 32bit operating system. win7 64bit will see all of it.
You can do it using bootcamp. see here.
Your laptop has some awesome specs, it should be fine for your purposes.
When you say it's running slow, is that when you are using Photoshop?
if so, got to preferences - performance, and check the memory usage, also check if your 'enable OpenGL drawing under the GPU settings, this will allow Photoshop to use the hardware acceleration of the graphics card.
If it's slow generally, ctrl alt delete - start task manager, click processes and just make sure nothing else is hogging your cpu (click the cpu column and it will sort by usage) - you may have an overly active anti-virus app or malware on there.
I regularly run a few apps to keep my pc running well,
spybot search and destroy
and I just use AVG. some other apps like norton internet security can slow you right down.
just watch out if any of them want to install toolbars etc - untick the ask toolbar etc when you do the setup.
might pay to put the cpu / memory meter gadget on your desktop (win7) so you can see at a glance what your cpu and memory status is. You don't want to get over about 75% on your memory usage, so if it does, something is hogging it.
hope this helps