Hopefully I can be of some help, being that I started at a support desk...
1. How do you deal with stressful situations? (in general help desks are stressful, how are you able to keep your cool when the lines light up... IT HAPPENS)
2. You are the firstone that people often talk to, they are pissed off/angry that thier CPU does not work, how will you deal with this? (IE, how can you appease them/ calm them down/no escalate thier feelings)
3. How do you interact with people over the phone, and what is one of the best ways you can talk with them to let them knwo you care about them? (smile when you talk... it comes through the phone)
4. What are you going to do between calls? We dont expect you to work like a banshee all the time, but we dont want you to fall asleep during the lulls, what can you do to fill your time constructivly?
5. What makes you a good team member?
6. Describe your work ethic?
7. How would you step a person through fixing a problem over the phone when you are not there to assist them physically? Methods? Information Gathering? Are you on the Same Page (is the problem understood).
Jsut a few for you to think about, but by no means the end all be all...