are you talking about your own server? The best way to hinder the os detection is to use the stealth iptables module i provide with grsecurity. Many of the techniques used in os fingerprinting depend on you sending a reply back that it can analyze.
check the date on the devel.grsecurity.net one, it hasn't been updated since november of 2001.
here's the one for grsecurity.net:
http://uptime.netcraft.com/up/graph/?mo ... it=Examine
it keeps switching back and forth from unknown to solaris
-Brad