Database backup not working :(

Hello,

Ive been trying to backup my DB for wordpress 2.0 upgrading but whenever I try to use the built in backup it doesnt work as the error tells me that the wp-backup-db folder is not writable.

What should be the chmod for this?

I also get this error too:

Warning: filesize(): Stat failed for /home/httpd/vhosts/marginalwalker.co.uk/httpdocs/wp-backup-db//1135878548_-_blog.sql (errno=13 – Permission denied) in /home/httpd/vhosts/marginalwalker.co.uk/httpdocs/wp-admin/database-manager.php on line 88

Warning: unlink(/home/httpd/vhosts/marginalwalker.co.uk/httpdocs/wp-backup-db//1135878548_-_blog.sql): Permission denied in /home/httpd/vhosts/marginalwalker.co.uk/httpdocs/wp-admin/database-manager.php on line 89