Why is it not possible to set the sidebar sizes in percentage? Currently it only accepts units of "pixels".

-- Brian

You can try adding it with a CSS insert

col.colone {
width: 20%;
}
col.coltwo {
width: 60%;
}
col.colthree {
width: 20%;
}

Thanks, this worked for me for Atahualpa. But now it caused an other error.
I use ata together with bytesforall. When I changed font size in bfa, the two sidebars increased together with the font size, while the center column shrinked. Now, the three areas holds their 20-60-20 percent size, but increasing the font size causes the page to grow over the screen (or browser window).

To see the error, visit my homepage: www.iszkaszentgyorgy.hu (FF 3.6/IE 8/Opera 10.60)
On the left side, click on "Vakbarát" (under "Kinézet"). (It is a modified BFA theme)
Now choose a different font size. (the default state can be restored by deleting cookie or going back with browser to the other theme)

Sorry, I use WP-chgFontSize, and selecting to change font size in pixels (rather than percent or em) solved the problem.