an 8800GTX was an awesome card... but that was 5 years ago
Working with Full HD video you need something with some guts. While you can get Graphic design cards, they are a specialty and modern GPU's can do the job just as well.
It all depends on the budget, a ATI 6850 or Nvidia 550 will set you back around £130-£150 and is a decent card, but not the fastest but will cope with it as well as modern gaming, you then have the next level ATI 6950 or Nvidia 560 or 570 for between £160 and £250. the next level up is the top end with the nvidia 580 and ATI 6970 £300+ or the extremes 590 and 6990 which are dual core beasties.. sooo youve got some choice.
If the bidget can stretch £80 more you can get a core i7 2600k, which is basically a hyperthread i5 2500k, so youve double the logical cores.
you then want A LOT of Ram and at a fairly decent speed id say a minimum of 8gb (16 if budget can stretch) and probably at a speed of 1666mhz or higher.
what im basically getting at is that you need a fairly high spec machine.. or time will be spent waiting for the computer to catch up.