choosing back up disc

[Aussie]

Re Time Machine... PPC 10.5, I would like to use Time Machine, have done some reading and indications are that you can choose a locality within the computer or obviously use an external HD. I don't have an external HD so thought when i clicked "Choose a back up disc" there would be options for internal storage but absolutely nothing comes up( the choice is greyed out). I have turned on the Time Machine but nothing changes and have searched the help menu.
Is this because there isn't enough room internally for the data to be saved? By most standards i don't have much on my computer, I particularly wish to save special mailboxes, iPhoto and a few documents. But i gather it also saves the whole system?
I don't wish to do any partitioning, want to keep it simple. And about external HDs is this something i need to go to an Apple specialist to buy or are they universal please?
Thank you.

 

[Kaveman]

There is no point doing a TimeMachine backup to the same disk that your backing up.

The reason you're backing up is to protect yourself from a failed HardDrive, which happens with terrible frequency, so why would you put it on a disk that will have failed?

Get a nice big external drive and hang it out the back via FireWire, if you can find an older enclosure with FireWire 400 on it.

 

[oldscribe]

Just to add to what Kaveman has said have a look here https://www.mac-help.com/t211710-backup-your-mac.html