You will need to remove the lower hard drive cage on the case. You will need a power drill with a 1/8" drill bit,
1. Remove the case front panel
2. After the front panel is removed, look at the lower bottom half part of the front of the case, you will see 6 rivets (You can sort of tell which are connected to the HDD cage)
3. Remove the rivets with the drill.
4. There is a couple screws you have to remove as well, one somewhere along the middle plate portion of the case.
5. Depending if your 800D is newly purchased or not, the old one will have a couple rivets on the INSIDE of the HDD cage which are very hard to get at, the drill won't reach it because of the middle panel.
6. To remove those rivets, you can use a dremel if you have one, or a chisel and hammer. (If you have the newer version of the case, it will not have these rivies)
Hope I explained well enough, I have the newer version of the case without the rivets on the inside of the cage, so I didn't have to deal with that.
Here is a detailed guide with pictures on how to remove it from Mr Armageddon: http://forum.corsair.com/forums/showthread.php?t=81698