Go to your Language Editor, sir
< As the man says ;)
Go to the language editor found under your network management area. Then select your language and then search for "member" then a seperate search for "membership" etc. and you can change all occurences of the words to any of your choosing
I also needed to do this and still can't find where to change where it counts the number of members in a group and lists it on each group - any ideas?