Operating System for a Built Server

What operating system is recommended for the running of a MySQL database and apache, and handle many clients?

I am running behind a router, and with Windows Home Edition on this PC I've had some problems forwarding ports to run a Ventrilo instance on it. I forward the ports fine, and the connection registers with clients, but they cannot enter the Ventrilo itself. I will be very angry if I invest in this primary database/query server and find that clients cannot connect. Perhaps it isn't the operating system and is simply something else, such as my firewall, but as a note, I followed Ventrilo's instructions to the letter.

Anyway, I seek not to make a ventrilo any longer, but I do need to be assured as possible that the operating system I purchase will allow connections.

I ask that you do not answer unless you are 100% certain of what you say, because I cannot afford a single mistake.

Perhaps one of the following?

Windows Server 2003
Windows Server 2008
Windows Server 2003/2008 Enterprise/Corporate Edition

Maybe even a version of Linux/Ubuntu? I have no biased for Operating Systems, I just need the dang thing to work, and work in a timely manner, which is why I am shying away a bit from Unix based systems because of their occasional requirement of emulation.

So, with that, I thank those in advance those who would don to answer this question.

Thanks again.