Here's how to figure it out from the Satoshi client code:
The IMPLEMENT_SERIALIZE macro is used to both store transactions on disk and to serialize them into a byte-array that can be hashed.
For class CTransaction, that looks like:
IMPLEMENT_SERIALIZE
(
READWRITE(this->nVersion);
nVersion = this->nVersion;
READWRITE(vin);
READWRITE(vout);
READWRITE(nLockTime);
)
READWRITE is a wrapper that is overloaded to Do The Right Thing for all the types bitcoin deals with; for complex types like CTxOut, IMPLEMENT_SERIALIZE is (essentially) called recursively.
Expand out all of the types and, assuming I didn't screw up (always an iffy assumption), it looks like a CTransaction is serialized as:
nVersion
vin.size (vectors are serialized as a compressed count immediately followed by their contents)
vin[].prevout (vin->prevout->hash followed immediately by vin->prevout->n, as 36 bytes)
vin[].scriptSig (CScripts are serialized as a vector of bytes)
vin[].nSequence
... repeated for each vin
vout.size
vout[].nValue
vout[].scriptPubKey
... repeated for each vout
nLockTime
String all those bytes together, SHA256 them twice, and you should get the transaction hash for the merkle chain.
