No you can only have one web server running at a time on the same port. Servers use port 80 and standard headers, pages and browsers look for that port.
Are you using NT 4.0? Set up Apache as a service.
go to services and shut down IIS and then start Apache or vice versa. It is possible to have one file root for both.
we run IIS but, I am really thinking of going over to apache. Can't afford the major cost of upgrade in Windows 2000
terry