Earlier versions of vBulletin had the function named as "fetchTableInfo"
If you want to get it working without updating your forum:
- Change "fetch_table_info" in line 885 of class_installer.php to "fetchTableInfo"
- Two lines down, change "add_field" to "addField"
Also, unless there's an easy way to skip ahead in the installer, or use an uninstaller (I didn't look into it) you'll have to do some table/column/row deleting in phpMyAdmin before the installer will go through again.