Because I can't. I've been trying to play C&C3 and Kane's Wrath on a fresh Windows install with no luck. I started off with a problem installing, then moved past that to a problem where the game would only run in low-res 4:3 mode with low graphics settings, then moved past that to a DirectX error crash on startup, then moved past that to a game that'll launch in 1920x1080 but the battlefield itself is white, nothing renders.

Here are the details:
BRAND NEW fresh Windows 7 64 bit install, fully updated.
Brand new installs of Tiberium Wars and Kane's Wrath, fully updated via the launcher update button.
Radeon 6870 with most recent drivers
Fresh, up-to-date installs of both DX9 and DX11.

Game launches just fine, menus look great, cutscenes play fine, UI elements all render, but the actual 3D battlefield elements are missing. Instead, the main battlefield area of the window is a huge swath of empty white, with UI elements like objective arrows overlaid.

I'm getting pretty damn pissed off at this. I spent HOURS yesterday just getting the games to install, then MORE hours getting to this point. But I've fixed everything there is to fix, and can't figure out what to do now. EA's support sites and forums are useless, Google turns up nothing. I'm at a loss. Has anyone else had this (these) problems before?

Here's a screenshot of what I've been dealing with:

That sucks. I had both those games installed on my laptop with Win7 64 bit and never ran into any issues like your having. They seemed to run pretty well. Before launching the game try right clicking the icon to see if it gives an option of which direct-x mode to run it in. I did that on my old laptop to play Crysis because it gave me the option of running it with directx 9 which made it perform better for me (just launching the game would default to directx 10). Granted, I was running Vista 64 bit on that laptop so that may not have anything to do with it but it's worth a shot.

Crysis' ability to run in DX9 or DX10 mode (in addition to choosing between 64 bit and 32 bit executables) is, unfortunately, a part of the game's design, and not something that can be enabled for just any program. Thanks for the suggestion, though. When I first got Crysis I was running a wimpy GTX260, so I ran it in DX9 mode as well, but with .cfg edited to allow for max settings under DX9.

I have tried running C&C3 in compatibility mode for XP SP3, but no luck.

Bizarrely, I've now found that, while C&C3 itself launches but has the above white screen problem, Kane's Wrath doesn't launch, and gives me an error about DX9 not being installed correctly. BOTH games' hardware autodetect (for graphics settings) think I have a terrible graphics card and warn me whenever I turn anything above minimum settings. I'm thinking it's a compatibility issue with my Radeon 6870.

Interesting. I used to play C&C with onboard graphics so try a 32bit Windows XP VM and see if it works?