AFP is usually provided by 3rd party software on Windows servers as far as I know. Windows usually uses SMB and/or CIFS, and you probably need 3rd party drivers to mount and use HFS and other Apple formatted drives. Never understood the need for any of it since OS X is happy dealing with all of the above as well as other file sharing systems like FTP to name but one.

As for NetBoot, this again would need 3rd party software I imagine. I guess if there is a an open source version of Server Admin or the netboot server component of it, you might be able to compile and run it from a PC running some kind of *NIX OS.
Netboot can be quite flaky even on Mac Servers, so I don't imagine it will be better (or even as good) on another OS. At least you can generate your boot images on the client and upload them, so you wouldn't have to worry about that.

The other way of doing it would be with an x86 hackintosh running OS X Server. Not even sure there is copies of such an OS in the wild yet, though unlike the client version, you can buy universal copies of Tiger Server. I'm told if you install regular PPC Tiger on a Mac and then download and run the Tiger Server Combo update using Pacifist, then you get a serial free copy of Server. I tried it once, but I forget how I got on.