Freezing posted in the blog a great guide to uploading to the rainbowduino. in the blog a usbuart was used but you can replace the parts that reference it with your usb tiny for the programmer.
here is the link to that blog post.
when you write to it, are you adjusting the fuse values? i had a rogue rainbowduino and had to redo the bootloader on it, you might need to redo that.