This is my wife's computer. I'm trying to save what she has set up already. If it was me using it I would have noticed it was running on Tiger before now.
I've gotten further with this though. Our two MacBooks are slightly different models--and the install discs are model specific. I looked through her box o' stuff that came from Apple and she had a Leopard Upgrade drop-in DVD. I used that to upgrade her system---and now her Mail is all wonky. It opens without opening a Mail Viewer, when I manually open a viewer her saved messages don't show up, it won't check mail, etc. It won't respond to the Quit command. Her saved mail is all in the correct place in the Library and her preferences all look right. I can't seem to find a way to just install Mail so I suppose I'm going to have to reinstall Leopard all over again to try to straighten it out.
Just for giggles, I used the Leopard drop-in DVD on another Mac and everything worked just fine.