Apache is another web server.<BR><BR>PWS is small time.<BR><BR>IIS is big time.<BR><BR>If you need these answers to be extrapolated, may I suggest going to http://www.microsoft.com and reviewing their extensive documentation? They do a much better job of explaining this than I can.
PWS is intended to allow you to develop sites in a lighter weight environment. It supports *most* of the features of IIS, but not all.<BR><BR>Notable elements not available in PWS include (but are not limited to)<BR>1) CDONTS<BR>2) Large numbers of connections<BR><BR>Other web servers ? Well there are hundreds, but if you want to use ASP, you are fairly limited to Microsoft products (though Chilisoft do a product for Apache).