Rev,
I feel your pain. I have two 750GB external drives to hold all the treasures.
You usually can't add an internal drive to a laptop, but you should be able to replace the current one with a larger version. You will need to either clone your existing drive to the new one and switch, or replace the drive and reinstall your OS. Once you have made the switch, you can wipe the old drive and put it in an external enclosure. That way you can maximize your storage space.
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