The specification details you should be closely looking at are, the CPU (Central Processing Unit), GPU (Graphic or Video Card(s), RAM (Memory), and Hard Disk Space.
It’s also worth look at connectivity; does the PC have FireWire IEEE 1394, 400/800, why FireWire, Isn’t that old hat technology now? It maybe to some degree, however, what if you want to revisit some of you older footage, shot on your trusty Mini DV camcorder? Are you archiving or backing up using an external hard drive, which is connected via FireWire, utilising the fast data transfer rates… if so, make sure the PC has FireWire connectivity, if not, is there a spare bay to slot in a FireWire card?
Alternatively, again being bang up to date, you could ask if the PC has the latest Super Speed USB, which is allegedly 10 times faster than USB 2. If the machine does not have this functionality, again you can buy Super Speed USB cards, if there is a spare PCi slot available to house this new additional card?
The CPU, i5 or ideally an i7 chip, these processors have been design with a huge bios towards coping with HD files, I am not knocking any dual or quad core processors, be they Intel or AMD chips, I am talking “ideal world” here, of course other chip will work with video editing, but you may get stuttering footage, crashes or freezes when trying to use/edit these HD files.
GPU Video/Graphics cards, advice pending!
Hard Disks (HDDs), most editing machine will have at least two hard drives, possibly even three. Budget permitting, you may wish to consider a Solid State HD for the operating system and editing software, solid state HD are phenomenally quick and far more robust than SATA drives, as with all new technology, they come at a heavy price premium, but well worth thinking about, budget permitting as the benefits of operating speeds and drastically reducing HD failure are such a big plus point.
RAM (memory), DDR3, the fastest consumer type memory, again it is very quick indeed, the more RAM the better, as far as I am concerned, ideally use an operating system which is 64bit, this gives a greater capacity to use more RAM, 4Gb, 8Gb, 16Gb, 32Gb I believe some systems even take 64Gb now... two factors which may govern how much RAM you go for, what your budget will run too, as well as what the max the motherboard will accommodate?
Finally, you have filmed your masterpiece, edited it successfully, now you want to output your movie to be enjoyed in all it’s splendour, therefore, you may wish to consider a Blue Ray burner/reader, this will allow you to produce a disc in “High Definition”, for all your friends family colleagues to enjoy, as long a they have HD TV’s and players?
