I just bought three 8 GB thumb drives to use as OS X, Linux, and Windows 7 installers.
I suppose you could split the thumb drive into two 8 GB partitions and create two installers. Whether or not both are visible on Macs and PCs is unknown. I suppose it will depend on the hardware.
To create the OS X installer, you need only run the following from Terminal.app. Note the partition name, I used "Untitled" for the script below.
/Applications/Install\ OS\ X\
/Volumes/Untitled --applicationpath /Applications/Install\ OS\ X\
To create the Windows installer, you take the Windows installation ISO file on a Mac, go here and scroll down to "Creating a Windows flash drive installer on an OS X computer".