Quad core = overkill
4gb ram = overkill
anything can do 1080p now days... its best done by hardware decoding with an integrated chipset and at the moment the AM2 motherboards are better at this.
If you are interested, you can take a look at my build
here... My E2200 does everything flawlessly at stock.
I would look at a board like this:
http://www.scan.co.uk/Product.aspx?WebProductId=775308 (has HDMI and onboard graphics that decodes Blu-ray)
and for the CPU:
http://www.scan.co.uk/Product.aspx?WebProductId=807038
any thing more powerful would work of course, but it is a waste of money...
if you go for intel, you will need a separate graphics card if you want hardware decoding
btw you should have posted this in the hardware forum... this forum is for abit presale/customer service