Install OS X on flash drive- "Essential System Software"?

I am trying to install Snow Leopard onto an 8GB flash drive to create a bootable drive. I formatted the flash drive with the GUID partition, made it bootable and everything. However, when I get to the Snow Leopard Installer screen where I have to choose a disk to install the OS on, it says that there is not enough space on my flash drive.

Even when I click the "Customize" button and uncheck all the optional software (printer drivers, languages, etc.) there is still an option called "Essential System Software" that is checked and unchangeable (grayed-out), and it takes up 8.01 GB.

What's stranger still is that when I try to install Snow Leopard +from the same screen+ onto my hard drive and I uncheck all optional installs, the same Essential System Software that took up 8.01 GB on my flash drive only takes about 3.3 GB now.

I've read all the tutorials online about how to do this. They all say that a shrunken-down Snow Leopard install should be about 3.6 GB, and that you only need an 8GB flash drive. And I can't find anything about this Essential System Software, anywhere. Does anybody know what it is or how to fix this?