The help desk can be a black hole for your career. If you have taken a help desk job at a start-up and someone uses the phrase: "In this position, you will need to wear many hats" in the interver, then heed my warning. If you are looking to apply the cool Perl knowledge you picked up, or utilize what you have learned the other night when you reached a state of pure technical perfection the instant you fixed that problem with your master boot record on your dual boot machine, then dust off your resume, its time to move to another job. Because, I assure you, your boss, as nice as he/she is doesn't have use for your adventures into programming and system administration and you should be getting paid to do the stuff you are staying up to 3AM to do.
Sure, you could stick it out and hope that possibly you will get that awesome project handed to you by a Senior Systems Administrator, but that is never going to happen. He would rather have you keeping end users out of his/her hair. And why not? As your company is growing they are going to want you to tell end users how to use their printers, and god forbid undo all the viruses that they downloaded, watching whatever young college coeds do when they get curious and there are a couple of barn animals and a midget (sorry small person) in the room.
I suggest you use the time that you are in this purgatory referred to as the help desk to really narrow down the things that you want to focus on. For example, I chose to focus on Linux, MySQL, and Perl. This will make me an awesome LAMP developer. I hone my craft every day. When you are ready, if there isn't a position in your company to move to, get yourself a new job. Because trust me, a good help desk guy/girl is hard to find. And if you are doing a good jobs at the help desk, then unless you make some big moves, they will do what they can to keep you there and away from the big servers where you belong.