I have a few questions....
Does this creaking noise become apparent only after driving for a while (at least 30-45 min)? If your issue is what I think it is, when you start the engine after sitting over night or after sitting for 2++ hours it should not make any noise.
Once the creaking is audible, turn the engine OFF and try to replicate the sound by pushing the clutch in and out. If you can still hear the creaking noise with the engine turned off, I can help you with your problem.
If you experience these symptoms, then you have more of an annoyance than an actual problem on your hands. A part of the clutch assembly called the release fork has a simple spring on it that dries out over time and needs lubrication. The problem is that it is nearly impossible to access unless you pull the trans...I have spoken to another fellow with the same issue who claimed to pull out the starter and was able to spray the spring with white lithium grease. I am a bit weary of this as I am worried the clutch disk will become contaminated with grease when I spray the spring.
Considering the relatively low cost of an entire new clutch assembly ($150), I plan on just replacing the whole thing. I figure that as long as I can put in the time myself I am saving most of the cost of a new clutch (labor$$$). I suppose before I replace the clutch I will look into the bellhousing to see if I can grease the spring...
The good news is that you shouldn't worry about this as it is really just an annoying sound. This is not like the noise a bad throwout bearing will make in the sense that a bad throwout bearing will in short time render the car un-drivable and potentially cause more costly repairs.
If you can live with the noise then by all means try to ignore it....if you have the time and tools you might want to look into taking apart the clutch and just replacing the components while you are down there. Good luck!