Building a Bitcoin IPN. Need unique identifier I am building a Bitcoin IPN to poll bitcoind every 5 minutes, find new payments with at least 1 confirm, and notify a server.

It looks like I am going to have to load them all up with 'listtransactions' every time and parse out new ones.  Inelegant, but I don't see any other option.

So the next problem is that I need a unique identifier of payments so that I can see if it has already sent a notice.  I have read that txid can change?  Well, that is not a bloody ID then, is it?!  How can I identify a payment?  sha1(address . amount . time) ?  What is the difference between 'time' and 'timereceived'? Are they static?

The best discussion I found about this is here but it doesn't look like it went anywhere;

https://bitcointalk.org/index.php?topic=3092.0

Cheers.
TXIDs cannot change. TXIDs are simply hashes of the transaction. It is possible for two different transactions to have the same TXID - that's called a hash collision. However, the chances of that happening are so low and I believe you will actually win prize money if you find a collision.