By coincidence, I mentioned this yesterday to a pal who just bought a
liveaboard and was mulling over getting a desktop for the nav station:

"Personally, I would go for the laptop for heat/power consumption
issues, and add components via FireWire/USB as needed. A desktop
underway pulls a large number of watts, you know, whereas a laptop
(like a used ThinkPad) is cheap, low-power, versatile and most
importantly, can be taken off the boat and NOT STOLEN. Unless you are
building a ship's safe, I would stick with a laptop I could slide into
the nav station in heavy weather. Their hard drives can stand the
movement better as well.

Now, what I would suggest is running remote mouse, keyboard and flat
screen from that laptop: Think this way: Turn on the laptop and stow
it safely in a padded nav station slot. Run a regular keyboard and
mouse to the nav table top. Get an armature with a light 15" LCD flat
screen monitor on it. Interface through SeaTalk with radar,
GPS/chartplotter, etc. Extend the armature with screen into the
companionway when underway, or mount it into the bulkhead (it's a
Naiagar 35 with a bulkhead at the base of the companionway). Put an
infrared receiver into the flat-screen housing. Put a wireless mouse
into your pocket.

Now, while sailing, you can switch between chartplotter, GPS, radar
and Internet by pointing and clicking at the screen that's five feet
in front of you and three times the size of the "integrated" displays
Raytheon, etc. sell. The PC itself is below, nice and dry. The
keyboard is stowed. The mouse is in your pocket. You have a totally
functional outfit, and yet you pull out three cords and you can take
the laptop ashore for safety, etc. You can also move the laptop into
the cabin to do your logs. You can back up to a portable hard drive or
burn "log" CD-ROMs.

Sound good? I have no clue why people buy dedicated $3000 multipurpose
units when a guy like your partner for instance could wire a bunch of
sending units to a circa-2001 $800 used laptop running Windows 2000
(don't use XP for mission-critical!)"

The bonus is that a two-year old laptop is far more likely to have a
serial port and yet will be plenty powerful enough to run all current
nav/charting software.

R.