Over on Macintouch's Mac OS X Reader Reports (well worth reading, as there's a ton of good info collected there!), Paul Christensen posted some information he received from Apple's tech support group regarding the initial setup assistant (which configures your primary user account, among other things).
According to Apple, to re-run the assistant, you need to:
mount -uw /
cd /private/var/db/netinfo
mv local.nidb local.old
rm ../.AppleSetupDone
exit
Mac OS X Hints
http://hints.macworld.com/article.php?story=20010827120222505