Actually you probably have used PWS but don't realize it. But for two registry entries, PWS is (or at least used to be) IIS. I don't know about Windows 2000, but with NT those two entries were the only difference between NT Workstation and NT Server.

Why 2 entries you ask? Well when there was just one they had too many problems with people just flipping it. So they made it 2 as a check, and if they don't match your computer will BSOD on boot. (To be sure, changing them violates your license agreement, so Microsoft does have a point...)

Anyways, any time you see PWS just say what you would think for IIS and it is probably going to be correct. It is the same software. Same binary. Just different configuration settings.