Doc - I'm pretty sure harpua wants to dual boot on a USB flash drive.
From what I've read, GParted can create multiple partitions on a flash drive. However, I've also read that Windows won't recognize more than one partition on a flash drive, which means that you can't create partitions with GParted and then copy the files in a Windows environment. But...it might be possible to create the partitions and use Linux to copy the files, like this:
Boot from the GParted disc, and partition one of the flash drives. Next, boot up a Linux distro, like the Ubuntu LiveCD. Plug in a flash drive (or use a second CD/DVD burner that has the CD/DVD you want to put on the flash drive) that has the files from the Windows 7 disc and copy those to one of the partitions on your newly created flash drive. Then, plug in the other flash drive that has the rescue files on it and copy those to the other partition. As long as both partitions have been created correctly, it might work.