If you want to select all users who are in group 117, you should use "!= 0", since "=1" will check to see if it is the first group listed, if a user belongs to multiple secondary groups. So if you want to change the password for all users who are in group 117, you should use this:
Code:
UPDATE vb3_user SET password=MD5(CONCAT(MD5('XXYYZZ1122'),salt)) WHERE FIND_IN_SET(117, membergroupids) != 0
If you aren't sure, you should have a backup first (at least a backup of the user table).