I'm not sure about 99x, but I do this all the time because I format constantly. What I do is, copy the files in the 2000x folder under the ICQ folder to a backup drive, when I reinstall/format, I install ICQ with my UIN number, shut down ICQ, copy the files I backed up into the 2000x folder, overwriting the existing files, open up the Database Converter, click on convert, and boom, ICQ is like I never formatted
Good luck