Hmm. The block is pretty simple, but when you start putting those triangles for the corners, you get weird measurements. Either the center square or the triangles can need to be cut with eighth inch measurements. Might be able to cut larger then trim down. Also, you need to be very careful that the corner triangles are cut so that the fabric straight of grain runs along the edges of the block.
Here's a tutorial for the basic square in square center:
http://quiltville.com/sqinsqtutorial.shtml