Hi all! I just thought I'd show everyone this awesome experiment on pumpkin preservation, as I don't think it's been linked yet. I carved mine on friday, and it had already shrivelled up something awful, so I soaked it in the bleach/cold water solution overnight, and it plumped right back up. I did this since I won't need it for very long anyway. Anyhow, enjoy:
How funny! I was just about to post a link to this project.
But for long term (year after year) preservation I'm really not sure. You could try sealing it with resin. They also sell carvable, artificial pumkins that are meant to be kept for years.