As a general guide only...
1. Configure two hard drives, and dedicate one to video editing
2. The video editing software you choose will determine what kind of graphics card would be good. Some v/e software takes advantage of the graphics card, others don't. In turn, the graphics card will largely determine the PSU.
3. A dual - or better - core CPU will generally be worthwhile. Some v/e software makes better use of this than others.
4. I think the amount of memory you configure will largely depend on your OS. No point configuring 12GB if you're using XP, for example, which can, IIRC, only use 3.5GB.