I really like the Palm as a platform but there doesn't seem to be much in the way of weather support out there.
This site offers some options for connecting your Palm to the internet while in flight. I've found some of the links to be dead so not sure how current the info is.
This site offers some cool aviation products in a Palm size format. It has the standard satellite and radar imagery but you can't overlay your position on it.
I use Co-Pilot for flight planning and Flight Master for moving map/navigation on my Palm T3. Now that Flight Master has terrain I'm hoping it's just a matter of time before he adds weather.
*Edit* I just found
this software which seems to be more in line with what you may be looking for.