Any quick dual-core and up PC will be able to handle HD movies with even a low end video card. Core 2 Duo 2.6 gig +, i3, i5, i7, Athelon x2, Phenom x4, x6 etc...
3-4 gig of RAM which is standard now almost in all computers, 1 tb drive for storage if you keep the movies on the drive, and a cheap video card like a Radeon 4350 will do the trick.