I'm in the process of playing with the Mikrotik hotspot feature. Use of this particular feature is a first for me and I will post news if I make any progress.
Anyone interested in trying it can download a 24-hour trial (yes!) from
http://www.mikrotik.com/download.html#v2
In most cases the CD image is easiest, just use it to boot a spare PC or laptop and follow the wizard. Note that it will completely wipe the hard disk of any computer you install it on so don't use it on your good PC!
All the documentation you can eat is online at
http://www.mikrotik.com/docs/ros/2.9/