Internet Information Services (IIS)
DSA Server, when installed for simple intranet usage with few users, can be installed where IIS is running. It will redirect its port to port 8000 (by default) and the users will have add that to their URL address for logins. Having the port be 8000 also creates extra steps when uploading Out of the Box reports to DSA Server.
More sophisticated installations, internet options, or a larger number of users require IIS to be disabled (and a dedicate machine or VM is recommended).
Server requirements and installation preparation: http://onlinehelp.tableausoftware.com/current/server/en-us/help.htm#requ.htm