user management software

Hello everyone,

I am looking for software that can tie in all of my software together. I want it so that when a user visits my website and logs in to my phpbb forum they are automaticall logged into my classifieds section as well and also my photohosting software and auctions. Whenever someone loggs into any of the above or changes there profile in any of the above I want the login or effected change to occur in all software.

does anyone have any thoughts on this?
I am pretty new to the web world and trying to learn as I go.
thank you all for any and all help,
sean