[all variants] Option key not working... problem for dual-booting

Hi.

I'm about to use my second Mac (a Macbook) with Ubuntu (or Kubuntu) as my main OS, keeping Mac OS just for the (very few and rare) things that I can only do with a Mac.

I'll use Boot Camp to do it. But I'm facing a problem:

My option key stopped working when I boot and I try to use it (for instance, to choose another startup disk or to reset the PRAM). It works normally when I'm using the computer afterwords (after signing in). Also, when my login screen appears, there are a bunch of dots filling in the password field, like if the computer was filling in the password itself (but it doesn't, I have to delete the chain of dots and enter my password). But this doesn't happen when I try (without success) to use the option key on boot.

The same happens when I press "C" to choose a CD as startup disk. The only way I have to startup from another disk is to go to Mac OS System Settings and choose a CD as the startup disk. With this I made a clean install of Mac OS, which led to nothing, since the option and other boot keys keep not working on boot.

But I could just boot from an Ubuntu installation CD using Mac OS Startup Disk settings and install Ubuntu. Then I just would have to choose the Boot Camp Ubuntu partition as a Startup Disk and it would always boot from Ubuntu. The problem is: how would I come back to Mac OS when needed? Is there any way of choosing a startup disk from within Ubuntu or Kubuntu? Or is there an alternative way of choosing the boot partition? Or a way to fix the option key problem?

Any help would be welcome.

Thanks