about 1.25 years ago i built a moderate video editing rig for the work i was doing, the rig in my sig, and chose intel because at that time they were better than amd at encoding, but am not sure about that anymore. what i found is that if the applications were smp/smt aware everything was excellent, but if there were not, i could not get cpu utilization over 50% because the os sees the ht p4s as 2 cpus. this was costly as i chose some software that unknowing to me and apparently the tech support of the company, it was not smt/smp aware.
other than that i chose to use most of the adobe suite for my needs, which turned out to be overkill as most stuff i do is just basic fades, no crazy weird video changes. i use ps for making any stills and you need atleast ps cs for a program that can stretch the pixel aspect ratio of a still for use in a 16:9 video and have it look good when played on widescreen display.
the 74GB raptor will be good for a system drive, but you will need a couple large sataII drives (if that chipset supports sataII, even if it doesn't get the sataII for future stuff as they are backward compatible with sataI) - say 250GB each because raw uncompressed DV video is large ~12GB/hour and i am sure hd stuff is much larger. but if you are using 1394/firewire to capture from a camera, the video is only coming in @ ~3.5MB/s so that is really no big deal.
as far as ram, i got away with 1GB, but again i am not really sure what you are doing as far as special effects, etc.
if i were to build this machine today, i would wait for the x2s to come down a bit and go that route w/ 2x1GB DDR, large sataII hdds and a 74GB raptor for a definate speed boost for the os/applications - i chose scsi for my system drive but that is me.
also you will need a dvd-burner - nec3520
sound card - depends on what you are doing
video card - not much needed unless you plan to game on this rig also
good quality(xclio, enermax, antec, ocz, fortron, etc) 500W ps as this machine will be stressed for hours at a time.
also when formatting use ntfs becase fat32 has a ~4GB limit on files size
after reviewing/reflecting a bit, you can easily build a nice machine for a decent price since you can get a nf4ultra board, a x2 cpu(personally i would hold out a bit for prices to drop, if you can), the ram is pretty cheap now since you don't need any special o/cing ram and hdds are pretty cheap too.