Backup your kOOL
It is quite simple to backup your kOOL installation - so do it ;-)
All you need is a copy of your database and of your web directory.
Backup your database
You can use mysqldump to backup your database:
mysqldump -u DB_USER -pDB_PASSWORD --quick DB_DATABASE > SAVE.sql
Where DB_USER, DB_PASSWORD and DB_DATABASE must be according to your kOOL setup. Then the whole database will be written to the file SAVE.sql in form of SQL statements. You might want to gzip or bzip2 the file.
You can use the following command to restore your database again:
mysql -u DB_USER -pDBPASSWORD -D DB_DATABASE < SAVE.sql
Backup your web directory
For backing up your web directory you can use any backup tool. A nice incremental backup tool is bontmia, a bash script based on rsync which produces incremental backup snapshots by using hard links.