Heh. I’ve got “dashboard problem” in admin area. For long. ))
Now it’s over.
When you see 404 page instead of your dashboard – and somethings like “admin.php?page=index.php” in your addressbar – you just need to go to your wp-content/plugins/ directory and rename index.php there to index.html
P.S. BTW WP2.7 adminpanel looks really great! Upgrade ASAP.