The accepted answer on How long was Jesus in the tomb? would only have been possible if the Last Supper was not the Passover meal, which I had always thought it was. Was the Last Supper in fact not the Passover meal?
My new understanding of the Last Supper is mostly based on the information at http://www.therefinersfire.org/celebrating_passover.htm.
The key verses which indicate that Christ was actually crucified on the day before the Passover feast are John 18:28 and John 19:14.
The day of preparation would be when they slaughter the Passover lamb, which would then be eaten that night.
Two things are clear from scripture:
There are a number of possible reconciliations of this. Some speculate that Jesus was a part of a minority Jewish sect that celebrated Passover on a different day. Others that he celebrated Passover a day early because he knew he wouldn't be able to do it on the right day (I don't know what Jewish Law would have said about that, but Jesus was never one to get hung up on legal technicalities).