As you may know, Worpdress 2.3 has a new database structure and therefore ical4wp does not work properly. Actually, everything is working except the list of ical feeds.
I took some time today and I fixed it, making sure that it continues to work with WP < 2.3 too.
I am not going to release a new version yet because I want to fix a few other things before but I know some of you are stuck with this WP upgrade, here is the function to replace the existing one (roughtly line 552 in ical4wp.php file):
Do not replace the all ical4wp.php file but only the ‘ical_list_calendars’ function inside ical4wp.php file.