You don't need to buy Win XP professional to have PWS.
I was actually able to install Web server extensions on Windows XP home edition by installing IIS components from NT 5.0 beta 2 version. Now, I have a mix of files that belong to both versions. When I checked the about box for PWS, I saw version 5.1 for PWS. Everything, works OK though. It even has FTP support like all real IIS' do.
I wonder if you can do the same thing using Win 2K option pack for these purposes