Read this: http://www.twistymegasite.com/forum/viewMsg.asp?ID=677
It's been awhile since I've looked at it, but this is what I can remember:
After having one in bits in my hands, I can tell you there is no safe way of taking a UFO apart because it's been glued together during assembly. That said, if you can figure out how to PULL on either a "tip" (the top or bottom pointy bits of the UFO) or an "edge" (the outer circumfrence) VERY HARD without destroying the puzzle, that piece will come off, you'll be able to disassemble the rest easily.
My suggestion is don't even try to disassemble it unless you can afford the loss of a piece.
Not that it's any help, but I believe it's much easier to reassemble one.