We used to do this for fun when I was a kid.
Get/make a cube mold (a small plastic box with dividers, like a pill box?)and line bottom with parchment paper. pack damp brown sugar as hard as you can into the mold to a single layer. Air dry the block.
The brown sugar cubes are generally made from raw cane sugar that has a molasses content of about 2%. The brown crystalized sugar you're thinking of is
I looked up the making of white sugar cubes; I've modified the only source I could find - the faq of the British Sugar company - to come up with this; similar to the recepie above.
Lay out granular white sugar on a clean, long board covered with paper or cling wrap and mist with water until sticky. Gather up the damp sugar, pack as hard as you can in the cube molds. Dry under a heat lamp, then continue to air dry before removing from molds.
http://www.britishsugar.co.uk/bsweb/bsgroup/faq.htm#Q%20How%20are%20sugar%20cubes%20made?We also used to make sugar crystals on strings - we'd take a peice of cardboard that can cover the mouth of a large jar (mayo jar, pickle jar, etc) and hang lots of strands of thread from it, tie the ends to a clean paperclip. (we'd dip the clip in alcohol to "sanitize" it) We'd boil up a teapot full of water and fill the jar; then start pouring sugar into the hot water until the water became super-saturated and the excess sugar began dropping to the bottom of the jar; almost 3 cups sugar to one cup water, if I remember right. Then we'd immediatly cover the jar with the cardboard, letting the threads dangle down into the hot water, put the jar into a out of the way spot and wait for 3 days to a week, depending on how cold it was. Crystals will have formed down the threads.
I have seen there's a few sites that decorate sugar cubes with frosting for special events - monogramed sugar cubes - weird...
http://www.sugarcubes.ca/sugarcubesmono.htmHave fun
Haele