My solution was to purchase a Toshiba laptop off of E-Bay. I knew only enough to make sure it had both serial and USB ports and a CD drive. I knew I could add memory(and have). The one shortcoming is the disk, you need a lot to store many charts. My solution will be to load them from the CD-ROM as I need them and delete the unused ones.
This will be my only electronic charting system. I have a Garmin eTrex on the laptop and a Garmin 12XL at the helm. When in use the laptop will be plugged into 12V even though it does have a battery. I have The Cap''n software and will buy a waterproof Pelican case to protect it all.