Help! Under spam attack, Need Help ASAP.

Hello,

I have a relatively new website and its been going pretty well for me until this last week when I have begun getting heavy spam attcks on a daily basis to my forum. Getting 15-2o spam comments a day (viagra/cialis, etc). I use wordpress but I dont know how to isolate these spam users from the legitimate users. I want to set the wordpress settings to filter these attacks out and not my users comments. Does anyone know how to do this??I use hostgator and wordpress. If this doesnt stop , it might ruin my website.

Any advice on what to do or where to go for help is appreciated.

Thanks.