Hey Frappuccino,

I was having the same problems with my brand new builds. Both machines are running 9800GTs. I went through 5 different vid cards and every nVidia driver I could find, but nothing worked. I finally stumbled onto a post on the main WoW boards.

My fix was to delete all of my config.wtf files, and let the game rebuild the video information. Apparently the file had gotten corrupted, most likely due to the fact that I haven't performed a clean install of WoW in about 4 years. Every time I upgrade hardware, I simply move my WoW folder around until everything is set up. I was just about to the point of completely formatting my machines and reinstalling WoW from scratch, but luckily this fixed the issue.

Now I can open 2, 3 or 4 windows at a time on my alt machines without any popping or tearing.

So my questions:
When was the last time you purged your temp data? Cache, WTF, Interface folders?
Do you move your folders around like me when you upgrade your hardware?

I did loads of testing and it all came down to "how can all these brand new video cards and identically built machines be faulty?". My biggest problem was that I built my new machines right before I installed the Wrath updates, so I wasn't thinking it could be the game client until I had exhausted all other possibilities.