Tested on 7.5.3, this'll give you the IPs for a given user. Replace # with your given UBBT table prefix, and ### with the ID number of the member you're interested in.
SELECT `#_POSTS`.`POST_ID`, `#_POSTS`.`POST_SUBJECT`, `#_POSTS`.`POST_POSTER_IP`, `#_USERS`.`USER_DISPLAY_NAME`
FROM `#_POSTS`,
`#_USERS`
WHERE `#_USERS`.`USER_ID` = `#_POSTS`.`USER_ID`
AND `#_USERS`.`USER_ID` = ###
It's not very clean, and there'll be repeats, but it's a start.