I'm a developer that is interviewing for a help desk support position. What are some things I should know that are different from normal developing? I've done troubleshooting on those systems, but don't have any help desk experience.
I've worked on a helpdesk before, and one of the most important things to realise is that it's not the easy option a lot of developers/systems administrators think it is.
It can also be unbelievably frustrating having a user on the phone, but being unable to help them and having to pass a case off to second or third line support. As has been said in other posts, communication skills are essential, especially if you're unable to see the screen of the user that you're supporting, and the person on the other end of the phone is non-technical.
Then again, it's a valuable learning experience and have thought a lot of support staff (and probably developers too) could learn a lot from spending some time on a helpdesk. It helps you empathise when you get support cases passed to you that don't have all of the information that you would like. It's also a great way to improve your own communication skills having to deal with users first hand rather than have the helpdesk act as a proxy between a developer and the user as happens in some cases.
I've also just come across an article on The Register which is a quite interesting read (especially the comments), for anyone considering working on a helpdesk
I've worked in a helpdesk team and the most important thing is mastering the art of communication! You need to have effective listening and communication skills (especially over the phone), since you're going to be facing customers. You should know how to manage "difficult" customers too. It can be very stressful at times, but you need to maintain a positive attitude.
Re-reading the question, since you'll be the one interviewed for the position.
Depending on the individual and environment, helpdesk support could be fun or disastrous for both the support personnel and end-users. You'll definitely have fun if you like what you're doing, which is "helping people". You MUST be patient enough to answer the same question twice (or 10-20 times). On the technical side, you might not be expected to but due to the amount of repetitious tasks, you'll want to always think about 'effectiveness' - this will drive you towards automating those tasks, and improvise solutions that will make your environment more productive.
Also, helpdesk people need to be able to effectively communicate by phone or in person. I believe that is one of the most sought out qualities for helpdesk support technicians. Google for some descriptions for helpdesk support positions and get an idea of what kind of abilities are required.