Don't do it.
Do not fucking do it.
My first Zen: A 30GB Nomad Xtra. Works like an absolute dream until the following things happen. 1: I install Creative's new firmware, making it so that no Zen will ever register with my PC again. 2: The headphone jack fucks up so there's only sound from one ear. 3: It will no longer charge due to a broken power port.
Second Zen: 40GB, same model. After realising that it wouldn't communicate with the PC I took it back. There's a thread I made somewhere about the music that was already on it, though.
Third Zen: I had the laptop by this point, so I could finally transfer music to a Zen. Hooray! Then one night the screen cracked. Overnight. A google search confirms that this is a frequent problem that Creative refuse to acknowledge. Its okay, I thought. It's on shuffle all. I'll live - then, one day, it just broke outright. I smashed it to pieces.
Fourth Zen: Actually my fiancée's. Zen V series. Again, all fine until the screen craps out - Do a Google search for "Dim orange screen of death". With no screen, if you change the music that's on it (necessary for a smaller size player) you can't put it back on shuffle all.
Fifth Zen: My fiancée currently has a Zen stone, and she's had no trouble with it. She's had it since December.
Me? I have a CD player now.