This is true. Cremation is forbidden for Orthodox Christians (except in places like Japan where burial is essentially impossible). A person who is cremated cannot be given an Orthodox funeral (unless it was done in ignorance or against the person's will, and even then it requires the bishop's express permission).
There are a number of reasons for this. For me, the most compelling is that it is plain sacrilege. We are both body and soul, combined in one single entity. To utterly dispose of the body through cremation, to us, is a denial of this reality. The body is not packaging, to be tossed away like so much debris. Man was created in the image and likeness of God, and that does not change simply because their soul has temporarily departed their body. It is not fitting that the image of God should be burned up, then violently pulverized into fine gravel. (I personally object to autopsy and embalming for the same reason—it's disrespectful to the body. Not all Orthodox agree on this detail, however.)
There is also the matter of the Resurrection. Salvation involves the entire universe, including our bodies which will be raised on the last day. While all humans will be raised regardless of their bodies' disposal, it is a symbolic denial of the resurrection to get rid of a body so there is basically nothing left.
Here are a couple of links with additional info:http://orthodoxinfo.com/death/cremation.aspxhttp://www.saintbarbara.org/faith/society/cremation.cfm