Faking OS detection

[leak () blackout ru]

I wonder how i can emulate some OS when somebody scans my box with
nmap -O or something else.
Im using FreeBSD on my servers, and currently i block all OS guessing
by setting
options TCP_DROP_SYNFIN in my kernel.

But is it possible to modify TCP/IP stack so it will emulate win2k or
linux or something else?

Thanx

-- 
// undef
// i code. therefore i am.