You're misunderstanding the way Time Machine works. With an OS X installation disc, or your recovery partition (in OS X Lion), you can always restore from a Time Machine volume.
No other solution needed. Built right into the operating system.
For OS X 10.6 and below, just insert the OS X installation disc shipped with your Mac. Boot into it by holding
C after startup. From Utilities, select Restore from Backup and point it to your Time Machine disk.
For OS X 10.7, boot your Mac into recovery mode (hold
Command-R at startup). Then, you can restore your system from the backup using the dialog that pops up.
As usual, for this to work, make backups to your Time Machine disk as often as you can. In case you have system installation DVDs, consider backing them up too. Discs easily get scratches or disappear. Note that you can also probably find installation discs … somewhere else on the internet in the unlikely event that you lost yours.
Always good to read: Mac 101: Time Machine and the Time Machine support pages.