In that case, you don't need a strong video card (which can be very expensive). Instead, you can concentrate building an quiet multimedia PC (you don't want to hear all those ventilators during the quite video moments).
Try these components or equivalent (budget $2000):
Processor Intel Core i7 920
Processor cooling Scythe Mugen 2 Rev. B
Motherboard Asrock X58 Deluxe3
RAM GeIL GV36GB1600C9TC (triple channel, 6GB)
Solid State Drives Intel Postville X25-M SSDSA2MH080G2R5 80GB
Hard disk Samsung EcoGreen F2 EG HD154UI, 1.5TB
HDD cooling Scythe Quiet Drive
Video card ATI HD5750 1GB GDDR5 PCI-E (with a Passive cooling!)
The rest of the components can be chosen based on the availability at your shop. Ask them for the good casing, 120mm ventilators and a good power unit.
The choice for an ATI video card will give you also the possibility to use multiple monitors (Eyefinity). For more info, look here: http://sites.amd.com/us/underground/products/eyefinity/Pages/eyefinity.aspx