The Voodoo 2 was the first 3D card I owned, so here's info from someone who used one:
1) Yes it should work. (Note the "Should".) The signal from your video card (IE: The Radeon) is taken out of the card, and then plugged into the Voodoo 2. From there, the signal is translated, 3Ded, then taken to the monitor. (NOTE: The Voodoo 2 is an accelerator card, and as such, does not output normal video-card signals, such as displaying Windows, like modern cards do. The Voodoo 2 will not enable you to have multiple monitor setups, as it is simply an accelerator, and not a true video card.)
2) Couldn't tell you for sure, but it works adequetly in a Windows 2000 enviroment, but it's not the best. For best results, use Windows 98.
3a) Graphics look equal to, or in some cases, better than the PSX edition of the game. It also runs the original Half-Life REALLY well at 1024x768! (Note: If you use two Voodoo 2s of the same type and brand, and link together using the included card-to-card link-cable, you can double the power of your card's 3D capabilities.)
3b) Yes and no. GlideFX, the video mode the driver uses, is routed through DirectX 5, using Direct 3D for it's graphics. By modern standards, no, it is not better than Direct 3D, but then again, it's also using a much earlier version of Direct 3D...
3c) The Voodoo 2 does NOT have AA.
3d) Not really... Yeah, it's a bit chunkier, but at a max rez of 640x480, it's not going to matter much. (Plus I get a lot of background problems when I use AA, so...)
Hope this helps!