NOTE: while the following instructions will still work there is a newer method available which is recommended please see:
I followed the steps over at this page http://poulsbo-karmic.angelfire.com/
for convenience i'll repost them up here in english but all credit for the fix goes to the original author.
Open a terminal and type:
tar -zxvf poulsbo1.tar.gzcd poulsbo1sudo ./install.plThen reboot, you should now be able to set the screen resolution to 1024x600.