New System

I am looking at new motherboard and cpu. Audio and Video are main uses. Any one have any ideas on dual core chip or single core Amd or Intel and which board. All ideas will be appreciated.

IMHO: AMD 64 for price reasons is the way. Getting a Motherboard that supports SLI is a good future-proofing technique. MSI Neo SLI is a great stable Motherboard whilst the DFI Lanparty SLI is the tweakers delight. As far as Dual vs Single core aside from heat dissapation there is no majorly noticable improvement on the 32 bit platform.

I'll take dual core of ANY brand than their single core counter parts.
Will I take dual core AMD over any CPU's available today? sure
Will I take dual core Intel over any single core AMD? Sure.

SLI/Crossfire are nothing but marketing.

Current Benchmarks Prove otherwise. Sure no games expressly support SLI, but come the day they do, I'll be happily playing them.

You say you'll be using your system for audio and video. What do you intend to do with audio and video? If it only means watching, you are fine with any modern CPU, even the cheapest Celeron/Sempron (assuming you don't want software decoding of HD video).

If you are into editing, you might want some serious CPU power. In that case, I'd really go for a dual core CPU. I think that in the near future, most editing softwares will be supporting dual core and thus improving the systems performance greatly.

AMD or Intel? I have to admit I've always been an AMD lover (oh that sounds so wrong.. I do have a live ) and for know I think there's no way around it. For the time being, the AMD64 CPUs (including the X2s) beat the Intel CPUs at about any point. Getting a X2 would be a safe choice.

Regarding the SLI/Crossfire matter: those are nice techniques, if you have an appliance for them. Put simply: if you are into heavy 3D gaming (new games at high resolutions and lots of FSAA), you might want to think about getting an SLI system. If not, forget about it. You might want to get an SLI enabled mainboard though, as they offer you the possibility to upgrade to SLI later, if you want to.

Good mainboards for the AMD64 series? If you are in a standard situation (let's say.. about 2 harddrives, 2 opticals, some videocard, 1Gb of memory and your CPU), you'll be fine with any regular mainboard. Get a brand like Asus, MSI, Gigabyte etc. If you need certain features, you may want to around for the board that features those.
Personally I quite like MSI, as they have always worked fine in my comps (but that doesn't say other brands aren't great too). The DFI boards are very nice too, esp if you are into overclocking. With an X2, don't get your overclocking hopes up...

Hope this helps a little