Q:

How to prevent dual booted OSes from damaging each other?

For better compatibility and performance in games I'm thinking about installing Windows additionally to Linux. I have security concerns about this, though. 
Note: "Windows" in the remaining text includes not only the OS but also any software running on it. Regardless of whether it comes included or is additionally installed, whether it is started intentionally or unintentionally (virus, malware).
Is there an easy way to achieve the following requirements:

Windows MUST NOT be able to kill my linux partition or my data disk

neither single files (virus infection) nor overwriting the whole disk

Windows MUST NOT be able to read data disk (-> extra protection against spyware)
Linux may or may not have access to the windows partition
both Linux and Windows should have full access to the graphics card

this rules out desktop VM solutions
for gaming I want the manufacturer's windows graphics card driver

Regarding Windows to be unable to destroy my linux install: this is not just the usual paranoia, that has happened to me in the past. So I don't accept "no ext4 driver" as an argument. Once bitten, twice shy. And even if destruction targeted at specific (linux) files is nearly impossible, there should be no way to shred the whole partition. I may accept the risk of malware breaking out of a barrier (e.g. VM) around the whole windows box, though.
Currently I have a system disk (SSD) and a data disk (HDD), both SATA. I expect I have to add another disk. If i don't: even better. My CPU is a Intel Core i5, with VT-x and VT-d available, though untested.
Ideas I've had so far:

deactivate or hide other HDs until reboot at low level

possible? can the boot loader (grub) do this for me?

tiny VM layer: load windows in a VM that provides access to almost all hardware, except the HDs

any ready made software solution for this? Preferably free.
as I said: the main problem seems to be to provide full access to the graphics card

hardware switch to cut power to disks

commercial products expensive and lots of warnings against cheap home built solutions
preferably all three hard disks with one switch (one push)

mobile racks - won't wear of daily swapping be a problem?

A:

I have almost the same problem (Hackintosh + Windows). The solution I found was installing another disk controller. These can be cheap ($30) or expensive (real RAID / SAS card on PCIe bus).
To the point:

Install Windows on its own disk. The motherboard SATA ports are good for this. (Leave the other controller plugged in.)
After Windows has been installed, disable (or don't install the driver) for the controller. Better: both. If the Windows kernel can't access the controller, it will not access the drive in there. This is much safer than disabling the disk in Windows.
Remove the Windows disk. (Against accidental deletion when installing other OSes.)
Install the other OS (Linux or whatever) on a disk on the controller. As *nix systems will not destroy other fs/disks on their own, no need to do anything here.
Plug the Windows disk back in (same motherboard port you took it out of).
Configure Grub to dual-boot.

In this configuration, you can access the Windows installation from *nix system, but Windows can't access anything that's on the controller.
That should be all.

A:

After upvoting kotekzot's answer and jet's comment here is the ultimate solution: buy a plain-old front-rack. Sorry, since shopping recommendations are forbidden I won't suggest you a specific brand.
Simply mount the system disk in the rack and swap at necessity. Since these things are cheap, you should consider buying two twin racks, because every model requires you to mount the disk in its unique enclosure that can be extracted at any time. So if you have a single rack and two enclosures you can swap disks at any time. Obviously be aware that if there are any other disks mounted on your desktop the OS has full access (super user principle) to all of them.
To run Windows in a way that it cannot access Linux partitions even after being infected by the worst malware ever, an alternate would be virtualizing, but obviously you won't get direct access to video card and gaming performance.

