That's weird, then.
My girlfriend installed Mandriva 2008.0, with official repositories, and the last version there is 2.0.0.6... What's the repository for your firefox 2.0.0.8 ?
Thanks for the answers.
EDIT: I found out what's wrong. The official repositories she was using are portuguese mirrors, which aren't as updated as other mirrors, as I found out. I changed it to French ones, rpmfind.net, and it updated Firefox to 2.0.0.8 and other programs also.
I'll try other repositories, because rpmfind.net sometimes is full of users and it can't work correctly, but at least I found and solved the problem.
Thanks for your help. Sorry for any inconvenience.