[Luca]

No, actually the hard drive is not a user-installable part. Replacing the hard drive yourself would void the warranty regardless of what you install. I'm not sure if Apple will replace your internal hard drive, but there's a company called MCE that might.

7200 RPM laptop drives really don't generate a whole lot more heat or draw more power than a 5400 RPM one. I wouldn't worry about it - if you upgrade, by all means get a 7200 RPM! It'll speed things way up.

Also, the largest capacity for a laptop drive has been 80 GB for a while now. I think it was in spring of this year that Seagate (I think) announced a 100 GB, 5400 RPM laptop drive, but it's still not very available yet. I recall desktop hard drives were stuck at 120 GB for quite some time, so give it a year or so and I bet you'll see 120+ GB laptop drives out. I wouldn't even be surprised if some companies stopped selling 4200 RPM hard drives, since they're so slow and being replaced with 5400 RPM ones.

I just checked MCE's store and it looks like they offer a hard drive upgrade service for the iBook but not the PowerBook. I know that the TiBook's hard drive was considered user-serviceable, but the AlBook's is not. It's a shame, really... majorly cuts down on the upgrade potential, since the hard drive is often one of the first things that needs to be upgraded (after RAM).