What version is your ICQ? ICQ 2001b Bulid #3659 and above will automatically restore you icq contact list. if your version of ICQ didn't restore you contact list, you do one of the following....
1. Copy the contents in 200x folder located in the ICQ directory to the newly installed 200x directory.
2. Copy the ICQ backup you made to the location where the newly installed ICQ will exist and then installing ICQ into that folder...