from the work on the release of WoW:C last year, and intel quad core and at least a HD 6870 or GTX 560. this is in the $800 range
HDD are very expensive due to flooding in Thailand. Western Digital's factory is still under 2 feet of water, still, and has been underwater for 3 months. Seagate is in a similar position, while Hitachi and Samsung get parts from that same area. MAYBE by 2013, prices will come down, don't expect that before then.
An SSD isn't NECESSARY, but will speed the loading of programs.
DVI is as good a picture quality as HDMI. HDMI just happens to also carry sound.
My general suggestion is an i5-2400 and an AS Rock H61M/U3S3 motherboard if you have no plans to overclock, which will save about $50-60 over an i5-2500K and the least expensive Z68 motherboard. 8 GB of DDR3-1333 RAM, a Hitachi 750GB drive (its $99 from newegg, and probably the best $/GB deal there right now), a GTX 560ti would be my recommended graphics card, behind a 500W to 600W 80+ or better PSU from Corsair, Antec, XFX, Seasonic, or Silverstone. OCZ, PC Power and Cooling, Xigmatek, and Enermax would be my 2nd tier of choice on PSU, then add a cheap DVD burner and whatever case that suits you, but stay under $50 for the case. Newegg has a Haanspree 23" 1920x1080 monitor for $139.99, but Acer and AOC also make good, inexpensive monitors
To answer your questions
1) Intel, simply faster
2) Flooding in Indonesia or some other far place on the other side of the world damaged a lot of HDD factories results in a huge price increase for us...first world problems (for us)...so try to reuse old ones if you want. you also dont neeed an ssd but its nice
3) DVI is better than HDMI, but it wont carry audio like HDMI
4) yup no problem with them.
AMD or Intel? -- Intel, UNLESS you plan to do "Let's play" videos or youtube walkthroughs, and then the AMD Phenom II 1100T becomes attractive.
Hard drive prices? -- As stated. Production is down and demand is up. It will normalize eventually.
DVI or HDMI? -- No real difference in terms of quality.
Bottom mounted PSU on a carpeted floor? -- Yes and no. You 'can' do it at the cost of reduced air flow and pulling particles from the carpet into your PSU/computer case. If you have filters installed over the air vents it does help to control the mess, but some overheating may occur. Worst case scenario is that you get a PSU full of fiber that eventually catches fire.
Can be done, yes, but I wouldn't personally recommend it. Just get a small plank or riser board to put on the carpet, then put the tower on top of that. Problem solved.