The three most important things to know about Desktop computing: Backup, Backup, Backup

Trivially simple these days with low costs for Hard Drives and DVD-Writers. Using either a 2nd Internal Hard Drive or an External Firewire Hard Drive, Total backups can be made on a Mac using Restore function (Applications, Utilities, Disk Utility), and on a PC with Backup (Start, All Programs, Accessories, System Tools).

Then data can be separately backed up to a DVD and stored offsite.