Motherboard vendors decided to get ready for Intel's Conroe processor by shipping i975X based motherboards with Conroe support.
The first one to acquire the desired Conroe compatibility appeared the D975XBX mainboard from Intel. It has been recently modified to support the upcoming Conroe: the corresponding mainboard revision is marked as 304 (D27094-304). You should remember though that neither 302 (D27094-302), nor 303 (D27094-303) mainboard revisions ensure compatibility with Conroe processors. The Intel D975XBX mainboard revision 304 started shipping on April 16, 2006.
The main difference is a new BIOS and the addition of ten resistors and two capacitors. More info over at X-bit Labs.