Well, you can use BitConverter to get to/from the underlying byte representation, but this will be in the machine's endianness - almost always little endian (except for itaniums).
If you have the byte[], you can just reverse it? Some subset of:
Code Snippet
double value = Math.PI;
byte[] buffer = BitConverter.GetBytes(value);
Array.Reverse(buffer);
double
newValue = BitConverter.ToDouble(buffer, 0);
(yes the above is a daft thing to do - just for illustration)
Note that Jon Skeet has an EndianBitConverter here that might be of use.
