Most motherboards support a HDMI output, you would have to have a fairly old or low end board not too have one.
If your mobo doesnt, your best off just buying a cheap graphics card to get the display output rather than replacing the mobo.
http://www.newegg.com/Product/Product.aspx?Item=N82E16814134157
Is your rig a pre-built (So from a HP, Dell, Best Buy type company) or is it custom? If it is a prebuilt, could you link to it?
Just there could be issues with form factor sizes.