Does installing Leopard format my comp?

I have an apple desktop and I just bought the Mac OS Leopard installation disk. I just wanted to ask, if I install the new Mac Leopard will my computer get formatted? (will my documents, applications, etc. get formatted) Do I have to backup my computer info on an external hard-drive?

thanks in advance

 

You can choose to Erase and Install or Upgrade. If you want to keep everything, then choose Upgrade .

 

That is a choice you make - normally you would do an upgrade install however, which keeps your applications and all your user data. Just beware, most of the issues with Leopard have been because of third-party applications that were not Leopard compatible having followed in an upgrade install - most applications will not cause any issues, but some will. I don't mean to dissuade you from upgrading, just want to warn you that if you get issues after the upgrade third-party programs are most likely to blame - and before any sort of major change in an operating system I definitely advise you to make a backup first. It should not be needed, but that's a poor excuse if something does happen

That came out rather more pessimistic than I had hoped, but well - make a backup, then upgrade install and you should be fine