How do you remove a Mac virus ?

I am a dumbass newbie on Macs and YES I actually clicked this, and have in my download file the Flip4mac WMV1.mpkg. It is still there in my downloads. I did not install but I no longer have sound. It just hums. i have a Mac OS X 10.5.7. If anyone can help, I will bless you past the date that iphones can cut and paste! MUCH THANKS! Admitted Dumbass Newb!