Are you talking about capturing digital video (ie. from a digital video camera), or analogue (Composite or S-Video)? A lot of motherboards these days come with on-board firewire (IEEE1394) ports which your digital camera plugs straight into. If not using a digital camera, then you could buy a TV tuner card which includes an S-Video or composite video IN.
Digital obviously is much better quality wise than analogue capturing.
I can put my digital camera in "AV converter mode", whereby it takes Composite or S-Video output from a VCR (for example), and converts it into digital "on the fly", thus allowing you to capture using Firewire.
If you don't have on board firewire, or dont wanna buy a new motherboard, you can get PCI firewire cards VERY cheap ($50 here in AUS).
There's a whole plethora (I've been waiting to use that word all week!!), of software to use for video editing. Often, you will get some form of video edit software if you buy a firewire card, or get a mobo with onboard firewire, but this software is often rubbishy low-end stuff.
Let me know if you're interested and I can give you a rundown on some of the stuff I've tried.