Block and Mitigate DDOS attacks on Windows

I recommend using - Anti-DDOS Guardian, which is capable of blocking basic DDOS attacks to systems which hosting some sort of HTTP Server.

Anti-DDOS guardian could be the only software which works well on x64 bit OS from MS Win Server 2003 to Win Server 2008.

There is another way to do the same by using WIPFW Firewall, a Win32 version of BSD IPFW Firewall. WIPFW will allow you to create firewall policies on advanced TCP flags which can mitigate DDOS attacks.

If you are on a 32 bit system and running Win Server 2003, go straight for "Sygate Personal Firewall PRO". Sygate can even detect port scans and block them.