Backup Solutions - Compressing Partition & Transfer

I administer a busy forum and require a best backup solution.
(Servers are clustered and running Debian Etch)

Currently when backup script packs the whole partition using command:
tar cvzf /backup/webroot/webroot-(today's-date).tar.gz /webroot
But, this causes huge load on to the server and the whole website becomes unavailable during this time.

Since the number of files is huge, it takes around 10-15min for it to finish.

Now, I need another software or a way to limit tar's load on to the system so that the website doesn't go down during the backup process.

(dd would work as /webroot has it's own partition but I'm not sure on how it the load goes with it and also if it works with cron)
Do you know any good solution?

Also, right now all backups are on each server separately.

To clarify, mysql server's backups are on mysql server and actual files' backups are on web server.

As you may have realized, this is very bad as it won't protect me from harddisk failures and hackings.

(Hacker can just delete the whole thing and website will be gone forever...)

So, to prevent them from happening and also for central management of the backups, I got a server just for backups.

Now, I need a way to transfer the backups to it.

What software do you recommend to accomplish this?
(scp, rsync, ncftp, etc...)

Some of you may say R1Soft's CDP is the best but I would like to have that as my last option because I don't want to rely on another company when it comes to backups.