In addition to the good advice elsewhere on this thread you might find the following links to be of use.
http://www.startuplessonslearned.com/2009/01/lean-hiring-tip... http://joelonsoftware.com/articles/FindingGreatDevelopers.ht... http://sites.google.com/site/steveyegge2/five-essential-phon...
You might also find this link to be useful, but I wrote it myself so ymmv http://fragile.org.uk/2010/03/anatomy-of-a-technical-intervi...