Are you using Rachshack? If you are being DOS'd or SYN there is NOTHING you can do. I have had this constantly and had to shutdown the online portion of my business due to these cyber terrorists (N). *shrugs* RS (and albet any other company) will just block your IP until the attack quits, costing you alot of money and potential customers.
Sadly, there is nothing that can be done when you are being attacked by multiple (spoofed) IPs at once. Heh, peeps say submit reports to the authorities (local police, fbi, homeland security). But unfortunately they currently do nothing for such a situation.