Regex for use with Buddypress?

Hello dear WPMU people,

we are desperatly trying to find out the correct Regex in "Show on approximate site to make the following?

Our URL are buddypress standard, like

.../members/alphateddy/groups/

We want to show a pop up when somebody first clicks on groups or on

http://gamebiz.club/members/alphateddy/media

etc

How do we set the conditions so that the usernames are getting stripped out?

The standard regex from a post below with ("sites")

or

/members/^([:alnum:])/groups?

are not working.

Thanks

- Marian