Adding items to furnidata have never been easier. It's all explained to you in the furnidata_xml. Here's an example.
Code:
<furnitype id="Sprite ID" classname="SWF Name">
<revision>Revision folder</revision>
<defaultdir>0</defaultdir>
<xdim>X-Coord</xdim>
<ydim>Y-Coord</ydim>
<partcolors>
<color>0</color>
<color>0</color>
<color>0</color>
</partcolors>
<name>Furniture name</name>
<description>Furniture description</description>
<adurl/>
<offerid>-1</offerid>
<buyout>1</buyout>
<rentofferid>-1</rentofferid>
<rentbuyout>0</rentbuyout>
<bc>1</bc>
<customparams/>
<specialtype>1</specialtype>
<canstandon>0/1</canstandon>
<cansiton>0/1</cansiton>
<canlayon>0/1</canlayon>
</furnitype>