Unfortunately, the LifeDrive will only accept a 4 GB drive, and even with the right size replacement drive, you have to follow some very complicated steps for the LifeDrive to boot from the replacement. You can see a step-by-step guide here.
I used to be a fan of the Palm OS, and I understand why many people are so loyal to it. Nonetheless, attempting to overhaul your LifeDrive will require you to pour lots of money into a final product that won't be nearly as capable as newer devices (like the iPad ) and may not even work at all if anything goes wrong during the upgrade. Palm OS devices were never designed to be "overhaulable," so I'm sorry but the smartest choice by far would be to move on to a different product.
If you could provide more info about what specific characteristics and abilities you are looking to achieve, we could make some recommendations about what might work well for you.
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