I built a X4 955/ASUS 78T-E system a week ago, for the very same kind of use as you're listing. Great combination - works like a charm and gives a Windows Experience of 7.3 (Vista: 5.9max; Windows 7: 7.9max) for the CPU. Your GPU is a dog - you'll want something faster for the HD video processing. I got an ASUS 9600GT SILENT - technology's already a bit dated, but it scores a still-good 6.8, has no fan, so it's completely silent, and it cost me only $70 (after rebate) from NewEgg.
You don't need 1600 RAM - 1333 is fine for Phenom II. Crucial has the best price-performance ratio right now, according to a recent test found elsewhere on Tom's.
You'll want a PSU with at least 450W for this combo - check you old one to make sure it's got it.
Except for the graphics card, I bought everything from ZipZoomFly as their package deal was clearly better.
BTW, OC'ing is a snap. It started getting instable around 3.8GHz, but I didn't fiddle much with the CPU voltages. Without changing anything else, you can safely OC it to about 3.7GHz as long as you keep an eye on CPU temp. I'm using the default AMD cooler and had no temp issues with it.
Thanks for the replies. I am really looking at buying a mobo with built-in video (with sideport memory). Sorry about not mentioning in my original post. I will probably not use my current video card in the new build.
Preferred Mobo with eSata, built-in GPU, ATX form factor.
I want to initially use the built-in GPU and within 6 months or so, when the prices drop, I will get a dedicated GPU.
I had considered i5, but after reading issues about 1156 problems (foxconn), I decided to stick with AMD. Also according to info gleaned from the internet, AM3 boards will likely support Core 6 CPUs, but Intel 1156 will not.