hey, thats great to hear, i was thinking of fidling with gentoo but can't really be bothered.
about the autostart, take a look at http://www.osnews.com/story.php?news_id=937 and see if you can understand the "user experience" section
I found a post on the gentoo forums that might have helped, but it was by you.... :P :P :P :P
between code listing 11 and 12 on the desktop page:
All that's left is to make sure that X comes up when Gentoo boots. Edit /etc/rc.conf so that DISPLAYMANAGER="kdm".
and make sure you follow listing 14: # rc-update add xdm default
hope that works