Newbie needs help with a mac virus and a custom scan

All,

I'm new to the forums and not particularly computer proficient, so please be gentle. 

I just got a virus where, under the threat column it reads "w32/autorun-abh," has a filename of "postcard.zip" and is asking me to remove it manually.  I'm on a Mac, and the instructions for removing it say to create a custom scan, select the area where it resides and then delete it.  This is where I'm lost.  I don't see where I create a custom scan and isolate it.  Can anyone help?

Thanks,

Mike