Best Snapshot Software for SBS 2003

Hi there

I have a couple of clients with Windows Small Business Server SBS 2003. They don't have the original operating system discs. I'm currently using NT Backup to backup Exchange, the System State and data files. However if the hard drive dies I will have no way to install SBS 2003 on it as its not available to download any more.

As a workaround, I was thinking about taking a snapshot/image of the server using a drive snapshot software like Drive Snapshot http://www.drivesnapshot.de , however I'm not sure if this will work and be successful should I need to restore.

Does anyone have any recommendations around free or budget friendly snapshot software which would take an image of the o/s incase the disks fail?

Also would it be recommended to take a snapshot often or would one snapshot suffice with regular NT system state backups etc?

Thanks in advance.