This Glide3 wrapper worked for me. Basically you put the dll in your Diablo2 directory and run the D2VidTest.exe and it'll let you select the Glide driver (which was used by the Voodoo3 cards back in the day). Then it'll wrap the Glide calls to OpenGL calls. This, of course requires you have a vid card which supports OpenGL, but who doesn't?
The wrapper also comes with a config utility (glide-init.exe) which you can run and there's an option for "desktop resolution" which will cause it to render full screen at your native resolution. It has to scale things a bit so it's a little blocky, but not bad (I run at 1440x900). It puts bars on the sides so that it's not all stretched out too.
I've been playing on Battle.Net with this without issue so far. And I don't see how it could be considered a hack or cheating, it's just a video card driver.