Okay, forgive me if this has already been said, as I didn't read all the pages of this thread...
If you accept that "voting legitimizes the state," then you have already accepted the State. The notion that voting makes the system legitimate is part of that system, and accepting that means accepting that system. And, more to the point, given the propensity for voting among the general population, if you accept that notion, then you have actually claimed that the State is legitimate.
An anarchist does not, by definition, accept the State as legitimate. No amount of voting, by anyone, including himself, will ever legitimize the State. It is an available tool, and can be used or not used, as he sees fit.
Voting is force, but that only restricts pacifists - not anarchists - from using it. If it is used for defensive purposes, then it is fully legitimate force, and not a violation of the ZAP. That is where the "ends" and the "means" come in. No ends can possibly justify aggression. However, no moral principle that I've ever heard of can restrict the use of non-aggressive force. Certain some folks (eg, pacifists) have aesthetic objections to the use of force, but aesthetics are personal and cannot be considered on-par with morality, which must be universal.
To sum up: here is nothing immoral about voting, per se, and no amount of voting can ever justify the existence of an aggressive entity, such as the State... there is no "principle" restricting anarchists from voting in defense of themselves or others against aggression. Only voting for aggression would be unprincipled.
Joe