Any modern PC less than 2 or 3 years old will generally be fine for video editing but the more powerful the better if you want to keep rendering times low. Two gig of ram will suffice. Lots of hard drive space is advised with a seperate drive for storing video on. If your camera is HDV then you will need more power ( at least 2 cores) as this video is less friendly to computers than DV video.
Video editing is one of the few things, as with games, that will really thrash any systewm so reliablity is important. I usually advise against any sort of overclocking for this reason.
You will only need a capture card if you wish to edit analogue sources such as vhs video or old old cameras.
You capture video and sound data via firewire with ALL tape based cameras. The data produced by tape cameras is superiour to hard drives, dvd, or SD card cameras. It is less compressed and far easier for editing apps to chew on.
I am not sure what you mean by ' blocks ' ?