I've done a bit of CSS hacking on the default theme to turn it into a 3 column layout. Click on the thumbnail for a pic:
This theme is based on the default theme from the 20070612 SVN version.
I also made some changes to the preview pane CSS to make it scroll horizontally if too wide.
I've tested it on Firefox2 and IE7.
IE6 will probably show some artifacts (at least one since I use the :first-child pseudo-class which IE6 does not support) or it might even look screwed-up altogether - I don't know; it's not installed on my PC
On IE7, the only glitch I have found so far is that the subject line will wrap over if it is too long to fit, obscuring the sender/recipient and date fields below it (
screenie).
Download here:
default_3column.zipFeel free to improve upon it!
Some technical details:
All changes are in mail.css except one letter difference in the mail.html template ('h' to 'v') to make the splitter vertically oriented.
The message list table cells are not rendered as table cells anymore, but are positioned 'absolute'. This was necessary to show two rows of info per message.