1. Do not require them to send resumes in Word, most of the open source people will be happy to send you a PDF, ODF file or point you to their online resume. If you insist they will rename a .html file to .doc and send that to you
2. Make sure your corporate website is readable with Firefox and adheres to open standards. If your site is requiring them to install all kind of proprietary plugins, they probably won't even look further.
3. Listing MS Office as a skills requirement is not a good idea.
Requiring documentation skills is.. but Open Source geeks prefer Latex or Docbook to write their docs.
4. Don't list other proprietary tools as job requirement, you are looking into hiring Open Source people, they probably know alternatives for the tools you list. Forcing people to use a tool they don't like never works out, either way.
5. Forget about Degrees , a self taught person with years of writing code and using it is worth much more to your organization than someone who proved he was capable of sitting on the school benches often reproducing what some retard who isn't fit for the industry thinks was cool 2 decades ago. However degrees don't hurt, but they shouldn't be a requirement.
6. Forget about Certifications too , Certifications are mostly a way to get more income from training for a software vendor. Most Certification exams are Multiple Choice and don't really prove a person is actually capable of implementing something. There are only a limited number of valuable certifications out there.
7. Don't expect that because their code is free they are free too. The average Unix guy might be 25-30% more expensive than the windows admin. But you only need 1 to manage 200 machines, not 20.
8. You need social skills also , yes there are bunch of people out there with no social skills, unless you need a Monkey force to write code and you have enough people capable of interacting with them.
9. Reward Open Source contributions , with conferences, a bonus etc
Stimulate an environment where Open source is not something that you use, but which you also create.
10. Do not create a history of violating licenses , but have a public record of good open source citizenship. If you are known to violate the GPL or related licenses Open Source people will hav doubts about why you need them or why they would be interested in creating a better product with you.