You did not mention your budget.
For video editing you need to run multithreaded application. So multicore processor will be good for you. Go for AMD Phenom II 920 or 940. For cheaper alternative, also look for the olde Phenom 9950BE processors.
You don't need a very high performance graphics card for Video editing. A decent Graphics card with fast memory (mainly GDDR3) will be fine. Don't be fooled by the 1 GB DDR2 versions of the graphics card. Here my choice is Palit 9800GT 512 MB @ 6.1k. Nvidia Graphics card supports CUDA technology which offloads the CPU work into GPU and most of the Editing softwares like Adobe, TMPGENC, Cybelink PowerToGo and many others support CUDA (ATI is also having ATI stream in their cards, but they are not widely supported yet). For cheaper alternative, go for Palit 9600GT 512MB GDDR3 @ 4.8k.
For AMD cards, go for PowerColour HD4850 512MB GDDR3 @ 6.6k.
FOr RAM increase your RAM by 2 GB. It will cost you around 1k. But before buying, please check the speed of your existing Ram and buy RAN of exactly same frequency. It will enable dual channel config in your ram and theoritically it will double the data transferred rate of your ram.
If you are buying 4850 or 9800GT ,you will be required a good PSU. FOr cheaper price go for Powersafe 500W Silver @ 1.8k.