Laptop on board...
Some Bias admitted: I have used a succession of Macs at home, from '92 onwards. I used the WinOS at my work (no choice in the matter) until I retired in '99. When the agency used IBM's, the hardware was bomb proof, the Dell replacements, otoh, died right and left. The Windows software had no hardware preference, it crashed regularly on all machines. Trivia -- the agency first used OS2, which seemed a lot more stable -- ancient history now.
I prefer the modern Unix-based MacOS.
I stopped running virus software after moving to OSX some years ago, and, while my 5 year old desktop G4 is the last dual-boot Mac, I have not had occasion to boot into system 9.x for over a year now.
Bold Statement: In general, either OS will probably meet your needs, and Linux might be a reasonable third choice if nav. software starts showing up for it.
Hardware observation: You can run all flavors of OS in "native" form on any newer Intel-based Mac.
FWIW, our next one will be a new 24" iMac for the home. We have had a G4 14" iBook for the boat and for land trips for the last couple years.
A Slot? In choosing a laptop, you would want to consider whether a slot is advantageous for you. The "Pro" notebooks from Apple have this, and the inexpensive MacBook (it replaced my iBook model) does not.
Since the WiFi/Airport card is standard inside, along with Bluetooth, I have never missed the slot.
Our charting software is from GPSNavX, and for this year I may upgrade to their $99. version that can auto-stitch charts on the fly as you move along. My present $40. version lacks this feature.
http://www.gpsnavx.com/
I started out by buying a chart CD, but now just d/l the ones from NOAA at no cost.
The USB WAAS GPS antenna is extremely sensitive and was under $100. It works inside the boat at the nav table, homing in on a full range of satelites.
On the WinOS navigation side there are cheap apps, some freebies, and the $600.+ Nobeltec application. I know that the later has a lot of interesting bells and whistles, and the local rep even did a nice demo for a group of us at the YC. I am still taken aback by the price. Their rep, BTW, was a really nice guy and focused on his product and it's features, even after discovering that the group was 1/4 Mac users.
(He got bonus points for having a sense of humor and avoiding any OS comparisons.)
We view movies, listen to music, do our word processing, and access the 'net from our YC, marinas, motels, etc. Last weekend I did a bunch of overdue system upgrades while visiting some friends with a DSL connection and WiFi in their house. The iBook took about 20 minutes to gulp down several hundred meg of files, and then (key point, here) demanded my password before installing ANY program, including stuff from Apple. I do like the security...
If you do go with Windoz, note that you could perhaps stay with XP for a long time -- MS just recently stopped supporting Win98...
Last summer at the NW rendezvous, we were aboard an E-35/3 with a laptop and a built-in HP printer (!). The teak woodwork around the printer was flawless. They were printing chartlets for each days run, lists of waypoints in case the computer quit during the day (they said that, not me), and generally really getting a lot of utility out of their computer.
I admit that I keep coveting that compact little Cannon $249. inkjet printer... Hmmmm.... It would fit so nicely on our nav table...
BTW, some folks that I know are putting Mini Macs on board, then putting an inexpensive LCD screen up and either using a wired keyboard and mouse or using Bluetooth for input devices.
For on-board power we use a small inverter and plug the computer power brick into it. Probably some efficiency loss in this 12vDC-to-110vAC-to-laptop brick dc converter, but it works fine.
Next I must come up a hold-down device for the iBook on the nav table. A friend with large Win laptop made some thin brass brackets, kind of straight-Z shaped, about 2" long. Thin enough to hold from each side of the case and still allow the lid to close and latch. I have sort of rulled out velcro... once you stick down a rigid item, like the bottom of the computer case, how would you "peel" it off? Yikes.
Do you already have a plan or a way to have 'net access when you are out on the water? My nav. program can d/l and use GRIB files, but once away from the marina WiFi source for a few days... no more 'net.
AIS: I have seen this working on a Mac, and it seems quite cool, but you have to add the AIS receiver black box (same for WinOS). It would be helpful to see the location and speed of the ferry approaching a narrow pass from around a rocky island, that cannot be seen yet on your radar..
Interesting topic for a cold rainy winter day. Responces should be fun. And, to think, we buy sailboats to be away from "too much technology." HA!
Happy Thanksgiving,
Loren in PDX