Help! Can't update from OS X 3.9...

Have iBook G4 (512mb; 1.33GHz)) bought about four years ago. Just bought iPhone 3G assuming my software was up-to-date, but seems Im on version 10.3.9, and should be on 10.4.11 (? need 4.10 anyway for the phone)!! How come the software updates didnt come through? When I go to updates now, it checks and says that everything is up-to-date but it clearly isnt. And of course iTunes is saying that ver. 8 is available but when I try to install it, the computer tells me i am actually up-to-date there too.
Do i need to buy OSX 10.4 from Apple? Do i need to download every version of 10.4 in sequence to get back up to speed? I can't find 10.4.0 on Apple support to carry on the sequence. If someone can help I would be so grateful (living on Tokyo so harder to get help here in English)
Thanks

OS 10.4 is a whole new version of OSX, it's called Tiger you are on Panther. You have to purchase it, just like if you want Leopard (10.5), you would have to purchase that as well.

You need to get retail copies of either Tiger 10.4 or Leopard 10.5. You should be able to get the disks off ebay, make sure they are retail disks, grey colored restore disks will most likely not run on your mac model

. Either will run on your Mac but with 512 meg of ram I would point to Tiger.

Once you have a new OS on there software update wil allow you to update the OS, although you can just download the combo update and update the OS all at once

Apple - Support - Downloads - Mac OS X 10.4.11 Combo Update (PPC) update for any version of Tiger


Apple - Support - Downloads - Mac OS X 10.5.5 Combo Update for Leopard