Here's a TechSoup article on the subject:
http://www.techsoup.org/howto/articlepage.cfm?articleid=401&topicid=10&btcfile=articlepage401

and here's a good primer from PNNOnline:
http://www.pnnonline.org/article.php?sid=4195

eBay has a starter guide at:
http://pages.ebay.com/community/charity/index.html

And finally, here's a book on the general topic of fundraising auctions (I haven't read it, though, so I can't vouch for it):
http://www.benefitauction.com/Book.htm

Robert