Docedison:
Did you install the tiny cores in 1.56 r2? 1.05 and 1.56 are two different IDE's...Doc
You don't need the tiny cores to program with the USBtinyISP -- it is an ISP programmer.
You do need to select it under "Tools|Programmer" before tryng to actually program with it using "File|Upload Using Programmer".
Note: Hitting the normal "Build and Upload" button won't work if you are using an ISP programmer. You need to use "File|Upload Using Programmer" instead.