Keyboard Navigation Question - Mail Grid Headers

Hi,

I'm trying to figure out how to provide access to grid headers in a mail 
grid via keyboard navigation.

When I read the instructions for a grid in

http://dev.aol.com/dhtml_style_guide#grid

the suggestion is that tabbing into the grid should land on the first 
cell, typically the grid header. However, for the email scenario, the 
tabbing action should probably land on the row corresponding to the 
first unread message or the most recent message (depending on the 
listing order).

The instructions then suggest implicitly that arrow key navigation would 
get you up and down, including up to the headers. However, that is not 
appropriate for a mail grid, where the user should be able to retain the 
message selection when they use the grid headers to resort the message 
list.

I was trying to figure out what Thunderbird does, but I have as yet 
failed to get to the message headers without actually clicking on them 
:) HOME goes to the first message (not the headers) which seems like the 
right thing to do, and using the up arrow from there does not do anything.

Appreciate any help, 

Ana