HD encryption primer questions

Howdy,

In my quest for a secure computing environment, I am considering encrypting all or part of my hard drives.

I am wondering, what are the pros/cons to doing this? I understand that some software requires pre-boot authentification, esentially locking the hard drive until the user is verified. This sounds good, but If a hard drive is encrypted and administrator logged in and on line, is the encrypted hard drive visible to a hacker?

I am interested in a public key encryption, can one get strong encryption with a public key sytstem? Any recomendations?

What amount of system resources will a fully or partially encryped drive soak up? We have a dual processor (XP pro 2G ram) machine that has recourses to spare, but we also have a 2.2ghz single processor (XP home 256 ram) machine that is resource challenged already.

Is HD encryption another software solution that is, like most software security, a band aid fix?

What are the benefits/drawbacks to encrypting part of a hard drive versus the whole drive?

Is there anything else I should be thinking about?

Thanks, again, in advance.

Sincerely,

Kevin