Sorry, I don't recommend it unless you sell your old cpu first. The only one worth having is the q6600, which I've seen for $60 used. If you find one in this price range, overclock it and use your old heatsink. Otherwise, wait and sell your old board/cpu/ram before ordering new parts. It's getting harder to unload socket 775 stuff where I live. The parts are too old. For ram, ddr2 still cost twice as much as ddr3, so I would stick with 4 gb; it's plenty for most applications. If you just can't wait to spend, get a 7xxx series video card so you can use it in your new build next year.
Upgrading to 8gb of RAM will not matter if you are running a 32 bit system, and, as stated from o1die, will most likely not make your computer too much faster. An SSD would help a lot with loading things faster. Assuming you have a PCI express slot available on your motherboard, the best upgrade I found for you (and for the least money) is this http://www.tigerdirect.com/applications/SearchTools/ite.... Obviously these cards are geared more towards gaming, but this should be a significant enough of an upgrade to be worth your money in video editing. Also, depending on what exactly your computer is struggling with as far as video editing goes, it is worth noting that if you need to render faster then it is a better idea to upgrade the CPU, because that is what does all the rendering of videos. Hope this helps.