Get fedora or Ubuntu, or Debian if you feel lucky.
Linux is what most webservers use, and combined with the BSD versions and Solaris it makes up pretty much the vast majority of web servers out there.
Apache on linux is very complex and it can be confusing, there are a lot more options for it (although I've never used Apache on Windows).
I don't know if it would be significantly better then Windows. Maybe, maybe not. Its going to take some effort. I don't think it would be worth it if your goal is just to run a web server, I dont' think that realy much in the way of significant performance advantages of Apache on Linux over Apache on Windows. It may be easier to keep good uptimes and good avaiblity as most Linux patches don't require you to reboot (only kernel updates realy require that) and maybe it will be more stable or secure. But I don't think that it's going to be that much better to just to do it for the sake of doing it.
But if you want to use it as a learning expernience then go ahead. You'd have a lot more options and stuff to use, apt-get on debian makes it simple to install complex setups. Lots more mods, more languages, more free software. It's going to be more flexible and with lot more server possiblities. (and it could always be significantly faster. I don't know of any benchmarks)
Play around with streaming media, learn how to remotely admin thru ssh, stuff like that.
If you don't like it, you can always go back to windows.