More information - the relevant M$ page
How to harden the TCP/IP stack, noting the high synattackprotect registry value can mess up voice and video services (that is, when set to value 2, the really hardened setting) - a decent hardware firewall should make the extreme value unnecessary, if properly configured.
AND service pack 1 of Windows 2003 Server includes an improved degree of TCP/IP stack hardening in defence against syn DoS attacks, which may supersede/(could even conflict with?) some of the tcp/IQ measures.
Thanks, Adam