Hi,
From what I've seen, the Fermi cards should be about the same size as the Tesla (C1060) cards. Upon comparison with my existing video / GPU's, they're the same width and length as a BFG GTX 285 card - sans water cooling block. For the height the card - it occupies two slots.
I'm planning on using the butt-ugly Lian Li 888 for my next build as well. Instead of using standard HDD's, I'll be going with SSD's for my build. I use a Silverstone TJ07 with my Tesla card now. On the motherboard, I have 2 - watercooled GTX 285's (lower two slots), and 1- Tesla C1060 card up top. They all fit, but there is not a lot of room to spare.
My challenges that came along with the Tesla card - I needed to upgrade the PSU (1600 Watt Silverstone) - which has a larger foot print that my previous PSU (1000 Watt Silverstone). Additionally, I moved from a Lang pump to an Iwaki RD/30 - that required moving around some components as well.
Good luck with your build!
Particleman529